diff --git a/build/Android.common.mk b/build/Android.common.mk
index fe24801..24bfe02 100644
--- a/build/Android.common.mk
+++ b/build/Android.common.mk
@@ -38,6 +38,7 @@
 	src/dex_instruction.cc \
 	src/dex_verifier.cc \
 	src/jni_compiler.cc \
+	src/jni_internal.cc \
 	src/memory_region.cc \
 	src/object.cc \
 	src/raw_dex_file.cc \
diff --git a/src/assembler_arm.cc b/src/assembler_arm.cc
index 91c259e..a519e35 100644
--- a/src/assembler_arm.cc
+++ b/src/assembler_arm.cc
@@ -1336,6 +1336,11 @@
   StoreToOffset(kStoreWord, src.AsCoreRegister(), SP, dest.Int32Value());
 }
 
+void Assembler::StoreRawPtr(FrameOffset dest, ManagedRegister src) {
+  CHECK(src.IsCoreRegister());
+  StoreToOffset(kStoreWord, src.AsCoreRegister(), SP, dest.Int32Value());
+}
+
 void Assembler::CopyRef(FrameOffset dest, FrameOffset src,
                         ManagedRegister scratch) {
   LoadFromOffset(kLoadWord, scratch.AsCoreRegister(), SP, src.Int32Value());
@@ -1468,8 +1473,7 @@
 }
 
 void Assembler::LoadReferenceFromStackHandle(ManagedRegister out_reg,
-                                             ManagedRegister in_reg,
-                                             FrameOffset shb_offset) {
+                                             ManagedRegister in_reg) {
   CHECK(out_reg.IsCoreRegister());
   CHECK(in_reg.IsCoreRegister());
   Label null_arg;
@@ -1477,8 +1481,8 @@
     LoadImmediate(out_reg.AsCoreRegister(), 0, EQ);
   }
   cmp(in_reg.AsCoreRegister(), ShifterOperand(0));
-  LoadFromOffset(kLoadWord, out_reg.AsCoreRegister(), in_reg.AsCoreRegister(),
-                 shb_offset.Int32Value(), NE);
+  LoadFromOffset(kLoadWord, out_reg.AsCoreRegister(),
+                 in_reg.AsCoreRegister(), 0, NE);
 }
 
 void Assembler::ValidateRef(ManagedRegister src, bool could_be_null) {
@@ -1489,7 +1493,7 @@
   // TODO: not validating references
 }
 
-void Assembler::Call(ManagedRegister base, MemberOffset offset,
+void Assembler::Call(ManagedRegister base, Offset offset,
                      ManagedRegister scratch) {
   CHECK(base.IsCoreRegister());
   CHECK(scratch.IsCoreRegister());
@@ -1499,13 +1503,4 @@
   // TODO: place reference map on call
 }
 
-// Emit code that will lock the reference in the given register
-void Assembler::LockReferenceOnStack(FrameOffset fr_offs) {
-  LOG(FATAL) << "TODO";
-}
-// Emit code that will unlock the reference in the given register
-void Assembler::UnLockReferenceOnStack(FrameOffset fr_offs) {
-  LOG(FATAL) << "TODO";
-}
-
 }  // namespace art
diff --git a/src/assembler_arm.h b/src/assembler_arm.h
index a20a40b..4fb061f 100644
--- a/src/assembler_arm.h
+++ b/src/assembler_arm.h
@@ -424,8 +424,9 @@
 
   // Store bytes from the given register onto the stack
   void Store(FrameOffset dest, ManagedRegister src, size_t size);
-
   void StoreRef(FrameOffset dest, ManagedRegister src);
+  void StoreRawPtr(FrameOffset dest, ManagedRegister src);
+
   void CopyRef(FrameOffset dest, FrameOffset src, ManagedRegister scratch);
   void LoadRef(ManagedRegister dest, ManagedRegister base, MemberOffset offs);
 
@@ -454,20 +455,13 @@
   void CreateStackHandle(FrameOffset out_off, FrameOffset handle_offset,
                          ManagedRegister scratch, bool null_allowed);
 
-  void LoadReferenceFromStackHandle(ManagedRegister dst, ManagedRegister src,
-                                    FrameOffset shb_offset);
+  void LoadReferenceFromStackHandle(ManagedRegister dst, ManagedRegister src);
 
   void ValidateRef(ManagedRegister src, bool could_be_null);
 
   void ValidateRef(FrameOffset src, bool could_be_null);
 
-  void Call(ManagedRegister base, MemberOffset offset, ManagedRegister scratch);
-
-  // Emit code that will lock the reference in the given frame location
-  void LockReferenceOnStack(FrameOffset fr_offs);
-
-  // Emit code that will unlock the reference in the given frame location
-  void UnLockReferenceOnStack(FrameOffset fr_offs);
+  void Call(ManagedRegister base, Offset offset, ManagedRegister scratch);
 
   // Emit data (e.g. encoded instruction or immediate) to the
   // instruction stream.
diff --git a/src/assembler_x86.cc b/src/assembler_x86.cc
index 6f833ad..35e6129 100644
--- a/src/assembler_x86.cc
+++ b/src/assembler_x86.cc
@@ -1413,6 +1413,11 @@
   movl(Address(ESP, dest), src.AsCpuRegister());
 }
 
+void Assembler::StoreRawPtr(FrameOffset dest, ManagedRegister src) {
+  CHECK(src.IsCpuRegister());
+  movl(Address(ESP, dest), src.AsCpuRegister());
+}
+
 void Assembler::CopyRef(FrameOffset dest, FrameOffset src,
                         ManagedRegister scratch) {
   CHECK(scratch.IsCpuRegister());
@@ -1546,8 +1551,7 @@
 
 // Given a stack handle, load the associated reference.
 void Assembler::LoadReferenceFromStackHandle(ManagedRegister out_reg,
-                                             ManagedRegister in_reg,
-                                             FrameOffset shb_offset) {
+                                             ManagedRegister in_reg) {
   CHECK(out_reg.IsCpuRegister());
   CHECK(in_reg.IsCpuRegister());
   Label null_arg;
@@ -1568,21 +1572,11 @@
   // TODO: not validating references
 }
 
-void Assembler::Call(ManagedRegister base, MemberOffset offset,
+void Assembler::Call(ManagedRegister base, Offset offset,
                      ManagedRegister) {
   CHECK(base.IsCpuRegister());
-  call(Address(base.AsCpuRegister(), offset));
+  call(Address(base.AsCpuRegister(), offset.Int32Value()));
   // TODO: place reference map on call
 }
 
-// Emit code that will lock the reference in the given register
-void Assembler::LockReferenceOnStack(FrameOffset fr_offs) {
-  LOG(FATAL) << "TODO";
-}
-// Emit code that will unlock the reference in the given register
-void Assembler::UnLockReferenceOnStack(FrameOffset fr_offs) {
-  LOG(FATAL) << "TODO";
-}
-
-
 }  // namespace art
diff --git a/src/assembler_x86.h b/src/assembler_x86.h
index 981141a..85cc50b 100644
--- a/src/assembler_x86.h
+++ b/src/assembler_x86.h
@@ -419,6 +419,7 @@
   // Store bytes from the given register onto the stack
   void Store(FrameOffset offs, ManagedRegister src, size_t size);
   void StoreRef(FrameOffset dest, ManagedRegister src);
+  void StoreRawPtr(FrameOffset dest, ManagedRegister src);
 
   void CopyRef(FrameOffset dest, FrameOffset src, ManagedRegister scratch);
 
@@ -455,19 +456,12 @@
   void CreateStackHandle(FrameOffset out_off, FrameOffset handle_offset,
                          ManagedRegister scratch, bool null_allowed);
 
-  void LoadReferenceFromStackHandle(ManagedRegister dst, ManagedRegister src,
-                                    FrameOffset shb_offset);
+  void LoadReferenceFromStackHandle(ManagedRegister dst, ManagedRegister src);
 
   void ValidateRef(ManagedRegister src, bool could_be_null);
   void ValidateRef(FrameOffset src, bool could_be_null);
 
-  void Call(ManagedRegister base, MemberOffset offset, ManagedRegister scratch);
-
-  // Emit code that will lock the reference in the given frame location
-  void LockReferenceOnStack(FrameOffset fr_offs);
-
-  // Emit code that will unlock the reference in the given frame location
-  void UnLockReferenceOnStack(FrameOffset fr_offs);
+  void Call(ManagedRegister base, Offset offset, ManagedRegister scratch);
 
   void AddImmediate(Register reg, const Immediate& imm);
 
diff --git a/src/calling_convention.cc b/src/calling_convention.cc
index 4760a8c..ae6ac25 100644
--- a/src/calling_convention.cc
+++ b/src/calling_convention.cc
@@ -7,6 +7,8 @@
 
 namespace art {
 
+// Managed runtime calling convention
+
 size_t ManagedRuntimeCallingConvention::FrameSize() {
   LOG(FATAL) << "Unimplemented";
   return 0;
@@ -30,21 +32,22 @@
   return GetMethod()->IsStatic() || (itr_position_ != 0);
 }
 
-size_t ManagedRuntimeCallingConvention::CurrentParamSizeInBytes() {
-  return GetMethod()->ParamSizeInBytes(itr_position_);
+size_t ManagedRuntimeCallingConvention::CurrentParamSize() {
+  return GetMethod()->ParamSize(itr_position_);
 }
 
 bool ManagedRuntimeCallingConvention::IsCurrentParamAReference() {
   return GetMethod()->IsParamAReference(itr_position_);
 }
 
+// JNI calling convention
 
 size_t JniCallingConvention::FrameSize() {
   // Return address and Method*
   size_t frame_data_size = 2 * kPointerSize;
   // Handles plus 2 words for SHB header
   size_t handle_area_size = (HandleCount() + 2) * kPointerSize;
-  return RoundUp(frame_data_size + handle_area_size, 16);
+  return RoundUp(frame_data_size + handle_area_size + SizeOfReturnValue(), 16);
 }
 
 size_t JniCallingConvention::OutArgSize() {
@@ -56,6 +59,12 @@
   return method->NumReferenceArgs() + (method->IsStatic() ? 1 : 0);
 }
 
+FrameOffset JniCallingConvention::ReturnValueSaveLocation() {
+  size_t start_of_shb = ShbLinkOffset().Int32Value() +  kPointerSize;
+  size_t handle_size = kPointerSize * HandleCount();  // size excluding header
+  return FrameOffset(start_of_shb + handle_size);
+}
+
 bool JniCallingConvention::HasNext() {
   if (itr_position_ <= kObjectOrClass) {
     return true;
@@ -108,12 +117,12 @@
   return FrameOffset(result);
 }
 
-unsigned int JniCallingConvention::CurrentParamSizeInBytes() {
+size_t JniCallingConvention::CurrentParamSize() {
   if (itr_position_ <= kObjectOrClass) {
     return kPointerSize;  // JNIEnv or jobject/jclass
   } else {
     int arg_pos = itr_position_ - (GetMethod()->IsStatic() ? 2 : 1);
-    return GetMethod()->ParamSizeInBytes(arg_pos);
+    return GetMethod()->ParamSize(arg_pos);
   }
 }
 
diff --git a/src/calling_convention.h b/src/calling_convention.h
index cf12692..4e2eab7 100644
--- a/src/calling_convention.h
+++ b/src/calling_convention.h
@@ -17,6 +17,8 @@
 
   bool IsReturnAReference() const { return method_->IsReturnAReference(); }
 
+  size_t SizeOfReturnValue() const { return method_->ReturnSize(); }
+
   // Register that holds the incoming method argument
   ManagedRegister MethodRegister();
   // Register that holds result of this method
@@ -66,7 +68,7 @@
   bool IsCurrentParamInRegister();
   bool IsCurrentParamOnStack();
   bool IsCurrentParamPossiblyNull();
-  size_t CurrentParamSizeInBytes();
+  size_t CurrentParamSize();
   ManagedRegister CurrentParamRegister();
   FrameOffset CurrentParamStackOffset();
 
@@ -77,10 +79,10 @@
 // | incoming stack args    | <-- Prior SP
 // | { Spilled registers    |
 // |   & return address }   |
-// | { Saved JNI Env Data } |
+// | { Return value spill } |     (live on return slow paths)
 // | { Stack Handle Block   |
 // |   ...                  |
-// |   length/link }        |     (here to prior SP is frame size)
+// |   num. refs./link }    |     (here to prior SP is frame size)
 // | Method*                | <-- Anchor SP written to thread
 // | { Outgoing stack args  |
 // |   ... }                | <-- SP at point of call
@@ -98,6 +100,9 @@
   size_t OutArgSize();
   // Number of handles in stack handle block
   size_t HandleCount();
+  // Location where the return value of a call can be squirreled if another
+  // call is made following the native call
+  FrameOffset ReturnValueSaveLocation();
 
   // Iterator interface
   bool HasNext();
@@ -105,7 +110,7 @@
   bool IsCurrentParamAReference();
   bool IsCurrentParamInRegister();
   bool IsCurrentParamOnStack();
-  size_t CurrentParamSizeInBytes();
+  size_t CurrentParamSize();
   ManagedRegister CurrentParamRegister();
   FrameOffset CurrentParamStackOffset();
 
diff --git a/src/common_test.h b/src/common_test.h
index 4531b39..ee22cb6 100644
--- a/src/common_test.h
+++ b/src/common_test.h
@@ -146,22 +146,23 @@
 //   native double fooDD(double x, double y);
 //   native Object fooIOO(int x, Object y, Object z);
 //   static native Object fooSIOO(int x, Object y, Object z);
+//   static synchronized native Object fooSSIOO(int x, Object y, Object z);
 // }
 static const char kMyClassNativesDex[] =
-  "ZGV4CjAzNQDuVKYsovltNxptaisjQasgppGak46k/n0sAwAAcAAAAHhWNBIAAAAAAAAAAJgCAAAS"
-  "AAAAcAAAAAUAAAC4AAAABQAAAMwAAAAAAAAAAAAAAAgAAAAIAQAAAgAAAEgBAACkAQAAiAEAANYB"
-  "AADeAQAA4QEAAOYBAADpAQAA7QEAAPIBAAD4AQAAAwIAABcCAAAlAgAAMgIAADUCAAA6AgAAQQIA"
-  "AEcCAABOAgAAVgIAAAEAAAADAAAABwAAAAgAAAALAAAAAgAAAAAAAAC0AQAABAAAAAEAAAC8AQAA"
-  "BQAAAAEAAADEAQAABgAAAAMAAADMAQAACwAAAAQAAAAAAAAAAgAEAAAAAAACAAQADAAAAAIAAAAN"
-  "AAAAAgABAA4AAAACAAIADwAAAAIAAwAQAAAAAgADABEAAAADAAQAAAAAAAMAAAABAAAA/////wAA"
-  "AAAKAAAAAAAAAGkCAAAAAAAAAgAAAAAAAAADAAAAAAAAAAkAAAAAAAAAcwIAAAAAAAABAAEAAAAA"
-  "AF8CAAABAAAADgAAAAEAAQABAAAAZAIAAAQAAABwEAcAAAAOAAIAAAAAAAAAAQAAAAEAAAACAAAA"
-  "AQABAAMAAAABAAMAAwAGPGluaXQ+AAFEAANEREQAAUkAAklJAANJSUkABExJTEwACUxNeUNsYXNz"
-  "OwASTGphdmEvbGFuZy9PYmplY3Q7AAxNeUNsYXNzLmphdmEAC09iamVjdC5qYXZhAAFWAANmb28A"
-  "BWZvb0REAARmb29JAAVmb29JSQAGZm9vSU9PAAdmb29TSU9PAAMABw4AAQAHDgAAAAEAB4GABIgD"
-  "AAACBQCAgAScAwaIAgABgAIAAYACAAGAAgABgAIAAYACAAAAAAwAAAAAAAAAAQAAAAAAAAABAAAA"
-  "EgAAAHAAAAACAAAABQAAALgAAAADAAAABQAAAMwAAAAFAAAACAAAAAgBAAAGAAAAAgAAAEgBAAAB"
-  "IAAAAgAAAIgBAAABEAAABAAAALQBAAACIAAAEgAAANYBAAADIAAAAgAAAF8CAAAAIAAAAgAAAGkC"
-  "AAAAEAAAAQAAAJgCAAA=";
+  "ZGV4CjAzNQA4WWrpXgdlkoTHR8Yubx4LJO4HbGsX1p1EAwAAcAAAAHhWNBIAAAAAAAAAALACAAAT"
+  "AAAAcAAAAAUAAAC8AAAABQAAANAAAAAAAAAAAAAAAAkAAAAMAQAAAgAAAFQBAACwAQAAlAEAAOIB"
+  "AADqAQAA7QEAAPIBAAD1AQAA+QEAAP4BAAAEAgAADwIAACMCAAAxAgAAPgIAAEECAABGAgAATQIA"
+  "AFMCAABaAgAAYgIAAGsCAAABAAAAAwAAAAcAAAAIAAAACwAAAAIAAAAAAAAAwAEAAAQAAAABAAAA"
+  "yAEAAAUAAAABAAAA0AEAAAYAAAADAAAA2AEAAAsAAAAEAAAAAAAAAAIABAAAAAAAAgAEAAwAAAAC"
+  "AAAADQAAAAIAAQAOAAAAAgACAA8AAAACAAMAEAAAAAIAAwARAAAAAgADABIAAAADAAQAAAAAAAMA"
+  "AAABAAAA/////wAAAAAKAAAAAAAAAH8CAAAAAAAAAgAAAAAAAAADAAAAAAAAAAkAAAAAAAAAiQIA"
+  "AAAAAAABAAEAAAAAAHUCAAABAAAADgAAAAEAAQABAAAAegIAAAQAAABwEAgAAAAOAAIAAAAAAAAA"
+  "AQAAAAEAAAACAAAAAQABAAMAAAABAAMAAwAGPGluaXQ+AAFEAANEREQAAUkAAklJAANJSUkABExJ"
+  "TEwACUxNeUNsYXNzOwASTGphdmEvbGFuZy9PYmplY3Q7AAxNeUNsYXNzLmphdmEAC09iamVjdC5q"
+  "YXZhAAFWAANmb28ABWZvb0REAARmb29JAAVmb29JSQAGZm9vSU9PAAdmb29TSU9PAAhmb29TU0lP"
+  "TwADAAcOAAEABw4AAAABAAiBgASUAwAAAwUAgIAEqAMGiAIAAaiCCAABgAIAAYACAAGAAgABgAIA"
+  "AYACAAwAAAAAAAAAAQAAAAAAAAABAAAAEwAAAHAAAAACAAAABQAAALwAAAADAAAABQAAANAAAAAF"
+  "AAAACQAAAAwBAAAGAAAAAgAAAFQBAAABIAAAAgAAAJQBAAABEAAABAAAAMABAAACIAAAEwAAAOIB"
+  "AAADIAAAAgAAAHUCAAAAIAAAAgAAAH8CAAAAEAAAAQAAALACAAA=";
 
 }  // namespace art
diff --git a/src/jni_compiler.cc b/src/jni_compiler.cc
index 67f8bc8..5385a8b 100644
--- a/src/jni_compiler.cc
+++ b/src/jni_compiler.cc
@@ -4,6 +4,7 @@
 #include <sys/mman.h>
 #include "src/assembler.h"
 #include "src/calling_convention.h"
+#include "src/jni_internal.h"
 #include "src/macros.h"
 #include "src/managed_register.h"
 #include "src/logging.h"
@@ -85,26 +86,54 @@
     jni_conv.Next();
   }
 
-  // 5. Acquire lock for synchronized methods. Done here as references are held
-  //    live in handle block but we're in managed code and can work on
-  //    references
-  if (native_method->IsSynchronized()) {
-    jni_conv.ResetIterator(FrameOffset(0));
-    jni_conv.Next();  // skip JNI environment
-    jni_asm->LockReferenceOnStack(jni_conv.CurrentParamHandleOffset());
-  }
-
-  // 6. Transition from being in managed to native code
+  // 5. Transition from being in managed to native code
   // TODO: write out anchor, ensure the transition to native follow a store
   //       fence.
   jni_asm->StoreImmediateToThread(Thread::StateOffset(), Thread::kNative,
                                   mr_conv.InterproceduralScratchRegister());
 
-  // 7. Move frame down to allow space for out going args. Do for as short a
+  // 6. Move frame down to allow space for out going args. Do for as short a
   //    time as possible to aid profiling..
   const size_t out_arg_size = jni_conv.OutArgSize();
   jni_asm->IncreaseFrameSize(out_arg_size);
 
+  // 7. Acquire lock for synchronized methods.
+  if (native_method->IsSynchronized()) {
+    mr_conv.ResetIterator(FrameOffset(frame_size+out_arg_size));
+    jni_conv.ResetIterator(FrameOffset(out_arg_size));
+    jni_conv.Next();  // Skip JNIEnv*
+    // Get stack handle for 1st argument
+    if (is_static) {
+      FrameOffset handle_offset = jni_conv.CurrentParamHandleOffset();
+      if (jni_conv.IsCurrentParamOnStack()) {
+        FrameOffset out_off = jni_conv.CurrentParamStackOffset();
+        jni_asm->CreateStackHandle(out_off, handle_offset,
+                                   mr_conv.InterproceduralScratchRegister(),
+                                   false);
+      } else {
+        ManagedRegister out_reg = jni_conv.CurrentParamRegister();
+        jni_asm->CreateStackHandle(out_reg, handle_offset,
+                                   ManagedRegister::NoRegister(), false);
+      }
+    } else {
+      CopyParameter(jni_asm, &mr_conv, &jni_conv, frame_size, out_arg_size);
+    }
+    // Generate JNIEnv* in place and leave a copy in jni_env_register
+    ManagedRegister jni_env_register =
+        jni_conv.InterproceduralScratchRegister();
+    if (jni_conv.IsCurrentParamInRegister()) {
+      jni_env_register = jni_conv.CurrentParamRegister();
+    }
+    jni_asm->LoadRawPtrFromThread(jni_env_register, Thread::JniEnvOffset());
+    if (!jni_conv.IsCurrentParamInRegister()) {
+      FrameOffset out_off = jni_conv.CurrentParamStackOffset();
+      jni_asm->StoreRawPtr(out_off, jni_env_register);
+    }
+    // Call JNIEnv*->MonitorEnter(JNIEnv*, object)
+    jni_asm->Call(jni_env_register, JniEnvironment::MonitorEnterOffset(),
+                  jni_conv.InterproceduralScratchRegister());
+  }
+
   // 8. Iterate over arguments placing values from managed calling convention in
   //    to the convention required for a native call (shuffling). For references
   //    place an index/pointer to the reference after checking whether it is
@@ -130,79 +159,7 @@
   }
   while (mr_conv.HasNext()) {
     CHECK(jni_conv.HasNext());
-    bool input_in_reg = mr_conv.IsCurrentParamInRegister();
-    bool output_in_reg = jni_conv.IsCurrentParamInRegister();
-    FrameOffset handle_offset(0);
-    bool null_allowed = false;
-    bool ref_param = jni_conv.IsCurrentParamAReference();
-    CHECK(!ref_param || mr_conv.IsCurrentParamAReference());
-    CHECK(input_in_reg || mr_conv.IsCurrentParamOnStack());
-    CHECK(output_in_reg || jni_conv.IsCurrentParamOnStack());
-    // References need handlerization and the handle address passing
-    if (ref_param) {
-      null_allowed = mr_conv.IsCurrentParamPossiblyNull();
-      // Compute handle offset. Note null is placed in the SHB but the jobject
-      // passed to the native code must be null (not a pointer into the SHB
-      // as with regular references).
-      handle_offset = jni_conv.CurrentParamHandleOffset();
-      // Check handle offset is within frame.
-      CHECK_LT(handle_offset.Uint32Value(), (frame_size+out_arg_size));
-    }
-    if (input_in_reg && output_in_reg) {
-      LOG(FATAL) << "UNTESTED";
-      ManagedRegister in_reg = mr_conv.CurrentParamRegister();
-      ManagedRegister out_reg = jni_conv.CurrentParamRegister();
-      if (ref_param) {
-        jni_asm->CreateStackHandle(out_reg, handle_offset, in_reg,
-                                   null_allowed);
-      } else {
-        jni_asm->Move(out_reg, in_reg);
-      }
-    } else if (!input_in_reg && !output_in_reg) {
-      FrameOffset out_off = jni_conv.CurrentParamStackOffset();
-      if (ref_param) {
-        jni_asm->CreateStackHandle(out_off, handle_offset,
-                                   mr_conv.InterproceduralScratchRegister(),
-                                   null_allowed);
-      } else {
-        FrameOffset in_off = mr_conv.CurrentParamStackOffset();
-        size_t param_size = mr_conv.CurrentParamSizeInBytes();
-        CHECK_EQ(param_size, jni_conv.CurrentParamSizeInBytes());
-        jni_asm->Copy(out_off, in_off, mr_conv.InterproceduralScratchRegister(),
-                      param_size);
-      }
-    } else if (!input_in_reg && output_in_reg) {
-      LOG(FATAL) << "UNTESTED";
-      FrameOffset in_off = mr_conv.CurrentParamStackOffset();
-      ManagedRegister out_reg = jni_conv.CurrentParamRegister();
-      // Check that incoming stack arguments are above the current stack frame.
-      CHECK_GT(in_off.Uint32Value(), frame_size);
-      if (ref_param) {
-        jni_asm->CreateStackHandle(out_reg, handle_offset,
-                                   ManagedRegister::NoRegister(), null_allowed);
-      } else {
-        unsigned int param_size = mr_conv.CurrentParamSizeInBytes();
-        CHECK_EQ(param_size, jni_conv.CurrentParamSizeInBytes());
-        jni_asm->Load(out_reg, in_off, param_size);
-      }
-    } else {
-      LOG(FATAL) << "UNTESTED";
-      CHECK(input_in_reg && !output_in_reg);
-      ManagedRegister in_reg = mr_conv.CurrentParamRegister();
-      FrameOffset out_off = jni_conv.CurrentParamStackOffset();
-      // Check outgoing argument is within frame
-      CHECK_LT(out_off.Uint32Value(), frame_size);
-      if (ref_param) {
-        // TODO: recycle value in in_reg rather than reload from handle
-        jni_asm->CreateStackHandle(out_off, handle_offset,
-                                   mr_conv.InterproceduralScratchRegister(),
-                                   null_allowed);
-      } else {
-        size_t param_size = mr_conv.CurrentParamSizeInBytes();
-        CHECK_EQ(param_size, jni_conv.CurrentParamSizeInBytes());
-        jni_asm->Store(out_off, in_reg, param_size);
-      }
-    }
+    CopyParameter(jni_asm, &mr_conv, &jni_conv, frame_size, out_arg_size);
     mr_conv.Next();
     jni_conv.Next();
   }
@@ -221,8 +178,55 @@
   jni_asm->Call(mr_conv.MethodRegister(), Method::NativeMethodOffset(),
                 mr_conv.InterproceduralScratchRegister());
 
+  // 11. Release lock for synchronized methods.
+  if (native_method->IsSynchronized()) {
+    mr_conv.ResetIterator(FrameOffset(frame_size+out_arg_size));
+    jni_conv.ResetIterator(FrameOffset(out_arg_size));
+    jni_conv.Next();  // Skip JNIEnv*
+    // Save return value
+    FrameOffset return_save_location = jni_conv.ReturnValueSaveLocation();
+    CHECK_LT(return_save_location.Uint32Value(), frame_size+out_arg_size);
+    jni_asm->Store(return_save_location, jni_conv.ReturnRegister(),
+                   jni_conv.SizeOfReturnValue());
+    // Get stack handle for 1st argument
+    if (is_static) {
+      FrameOffset handle_offset = jni_conv.CurrentParamHandleOffset();
+      if (jni_conv.IsCurrentParamOnStack()) {
+        FrameOffset out_off = jni_conv.CurrentParamStackOffset();
+        jni_asm->CreateStackHandle(out_off, handle_offset,
+                                   mr_conv.InterproceduralScratchRegister(),
+                                   false);
+      } else {
+        ManagedRegister out_reg = jni_conv.CurrentParamRegister();
+        jni_asm->CreateStackHandle(out_reg, handle_offset,
+                                   ManagedRegister::NoRegister(), false);
+      }
+    } else {
+      CopyParameter(jni_asm, &mr_conv, &jni_conv, frame_size, out_arg_size);
+    }
+    // Generate JNIEnv* in place and leave a copy in jni_env_register
+    ManagedRegister jni_env_register =
+        jni_conv.InterproceduralScratchRegister();
+    if (jni_conv.IsCurrentParamInRegister()) {
+      jni_env_register = jni_conv.CurrentParamRegister();
+    }
+    jni_asm->LoadRawPtrFromThread(jni_env_register, Thread::JniEnvOffset());
+    if (!jni_conv.IsCurrentParamInRegister()) {
+      FrameOffset out_off = jni_conv.CurrentParamStackOffset();
+      jni_asm->StoreRawPtr(out_off, jni_env_register);
+    }
+    // Call JNIEnv*->MonitorExit(JNIEnv*, object)
+    jni_asm->Call(jni_env_register, JniEnvironment::MonitorExitOffset(),
+                  jni_conv.InterproceduralScratchRegister());
+    // Reload return value
+    jni_asm->Load(jni_conv.ReturnRegister(), return_save_location,
+                  jni_conv.SizeOfReturnValue());
+  }
+
   // 11. Release outgoing argument area
   jni_asm->DecreaseFrameSize(out_arg_size);
+  mr_conv.ResetIterator(FrameOffset(frame_size));
+  jni_conv.ResetIterator(FrameOffset(0));
 
   // 12. Transition from being in native to managed code, possibly entering a
   //     safepoint
@@ -230,21 +234,10 @@
                                   mr_conv.InterproceduralScratchRegister());
   // TODO: check for safepoint transition
 
-  // 13. Move to first handle offset
-  jni_conv.ResetIterator(FrameOffset(0));
-  jni_conv.Next();  // skip JNI environment
-
-  // 14. Release lock for synchronized methods (done in the managed state so
-  //     references can be touched)
-  if (native_method->IsSynchronized()) {
-    jni_asm->UnLockReferenceOnStack(jni_conv.CurrentParamHandleOffset());
-  }
-
   // 15. Place result in correct register possibly dehandlerizing
   if (jni_conv.IsReturnAReference()) {
     jni_asm->LoadReferenceFromStackHandle(mr_conv.ReturnRegister(),
-                                          jni_conv.ReturnRegister(),
-                                          jni_conv.CurrentParamHandleOffset());
+                                          jni_conv.ReturnRegister());
   } else {
     jni_asm->Move(mr_conv.ReturnRegister(), jni_conv.ReturnRegister());
   }
@@ -263,6 +256,86 @@
   native_method->SetCode(code.pointer());
 }
 
+// Copy a single parameter from the managed to the JNI calling convention
+void JniCompiler::CopyParameter(Assembler* jni_asm,
+                                ManagedRuntimeCallingConvention* mr_conv,
+                                JniCallingConvention* jni_conv,
+                                size_t frame_size, size_t out_arg_size) {
+  bool input_in_reg = mr_conv->IsCurrentParamInRegister();
+  bool output_in_reg = jni_conv->IsCurrentParamInRegister();
+  FrameOffset handle_offset(0);
+  bool null_allowed = false;
+  bool ref_param = jni_conv->IsCurrentParamAReference();
+  CHECK(!ref_param || mr_conv->IsCurrentParamAReference());
+  CHECK(input_in_reg || mr_conv->IsCurrentParamOnStack());
+  CHECK(output_in_reg || jni_conv->IsCurrentParamOnStack());
+  // References need handlerization and the handle address passing
+  if (ref_param) {
+    null_allowed = mr_conv->IsCurrentParamPossiblyNull();
+    // Compute handle offset. Note null is placed in the SHB but the jobject
+    // passed to the native code must be null (not a pointer into the SHB
+    // as with regular references).
+    handle_offset = jni_conv->CurrentParamHandleOffset();
+    // Check handle offset is within frame.
+    CHECK_LT(handle_offset.Uint32Value(), (frame_size+out_arg_size));
+  }
+  if (input_in_reg && output_in_reg) {
+    LOG(FATAL) << "UNTESTED";
+    ManagedRegister in_reg = mr_conv->CurrentParamRegister();
+    ManagedRegister out_reg = jni_conv->CurrentParamRegister();
+    if (ref_param) {
+      jni_asm->CreateStackHandle(out_reg, handle_offset, in_reg,
+                                 null_allowed);
+    } else {
+      jni_asm->Move(out_reg, in_reg);
+    }
+  } else if (!input_in_reg && !output_in_reg) {
+    FrameOffset out_off = jni_conv->CurrentParamStackOffset();
+    if (ref_param) {
+      jni_asm->CreateStackHandle(out_off, handle_offset,
+                                 mr_conv->InterproceduralScratchRegister(),
+                                 null_allowed);
+    } else {
+      FrameOffset in_off = mr_conv->CurrentParamStackOffset();
+      size_t param_size = mr_conv->CurrentParamSize();
+      CHECK_EQ(param_size, jni_conv->CurrentParamSize());
+      jni_asm->Copy(out_off, in_off, mr_conv->InterproceduralScratchRegister(),
+                    param_size);
+    }
+  } else if (!input_in_reg && output_in_reg) {
+    LOG(FATAL) << "UNTESTED";
+    FrameOffset in_off = mr_conv->CurrentParamStackOffset();
+    ManagedRegister out_reg = jni_conv->CurrentParamRegister();
+    // Check that incoming stack arguments are above the current stack frame.
+    CHECK_GT(in_off.Uint32Value(), frame_size);
+    if (ref_param) {
+      jni_asm->CreateStackHandle(out_reg, handle_offset,
+                                 ManagedRegister::NoRegister(), null_allowed);
+    } else {
+      unsigned int param_size = mr_conv->CurrentParamSize();
+      CHECK_EQ(param_size, jni_conv->CurrentParamSize());
+      jni_asm->Load(out_reg, in_off, param_size);
+    }
+  } else {
+    LOG(FATAL) << "UNTESTED";
+    CHECK(input_in_reg && !output_in_reg);
+    ManagedRegister in_reg = mr_conv->CurrentParamRegister();
+    FrameOffset out_off = jni_conv->CurrentParamStackOffset();
+    // Check outgoing argument is within frame
+    CHECK_LT(out_off.Uint32Value(), frame_size);
+    if (ref_param) {
+      // TODO: recycle value in in_reg rather than reload from handle
+      jni_asm->CreateStackHandle(out_off, handle_offset,
+                                 mr_conv->InterproceduralScratchRegister(),
+                                 null_allowed);
+    } else {
+      size_t param_size = mr_conv->CurrentParamSize();
+      CHECK_EQ(param_size, jni_conv->CurrentParamSize());
+      jni_asm->Store(out_off, in_reg, param_size);
+    }
+  }
+}
+
 void* JniCompiler::AllocateCode(size_t size) {
   CHECK_LT(((jni_code_top_ - jni_code_) + size), jni_code_size_);
   void *result = jni_code_top_;
diff --git a/src/jni_compiler.h b/src/jni_compiler.h
index 4a6b1ba..48666aa 100644
--- a/src/jni_compiler.h
+++ b/src/jni_compiler.h
@@ -3,6 +3,7 @@
 #ifndef ART_SRC_JNI_COMPILER_H_
 #define ART_SRC_JNI_COMPILER_H_
 
+#include "calling_convention.h"
 #include "globals.h"
 #include "macros.h"
 
@@ -19,7 +20,14 @@
   JniCompiler();
   ~JniCompiler();
   void Compile(Assembler* jni_asm, Method* method);
+
  private:
+  // Copy a single parameter from the managed to the JNI calling convention
+  void CopyParameter(Assembler* jni_asm,
+                     ManagedRuntimeCallingConvention* mr_conv,
+                     JniCallingConvention* jni_conv,
+                     size_t frame_size, size_t out_arg_size);
+
   // A poor man's code cache
   void* AllocateCode(size_t size);
 
diff --git a/src/jni_compiler_test.cc b/src/jni_compiler_test.cc
index 59d8c2b..23615ed 100644
--- a/src/jni_compiler_test.cc
+++ b/src/jni_compiler_test.cc
@@ -163,6 +163,22 @@
   }
 }
 
+int gJava_MyClass_fooSSIOO_calls = 0;
+jobject Java_MyClass_fooSSIOO(JNIEnv*, jclass klass, jint x, jobject y,
+                             jobject z) {
+  EXPECT_EQ(3u, Thread::Current()->NumShbHandles());
+  EXPECT_EQ(Thread::kNative, Thread::Current()->GetState());
+  gJava_MyClass_fooSSIOO_calls++;
+  switch (x) {
+    case 1:
+      return y;
+    case 2:
+      return z;
+    default:
+      return klass;
+  }
+}
+
 TEST_F(JniCompilerTest, CompileAndRunNoArgMethod) {
   scoped_ptr<DexFile> dex(OpenDexFileBase64(kMyClassNativesDex));
   scoped_ptr<ClassLinker> linker(ClassLinker::Create());
@@ -387,4 +403,57 @@
   EXPECT_EQ(7, gJava_MyClass_fooSIOO_calls);
 }
 
+TEST_F(JniCompilerTest, CompileAndRunStaticSynchronizedIntObjectObjectMethod) {
+  scoped_ptr<DexFile> dex(OpenDexFileBase64(kMyClassNativesDex));
+  scoped_ptr<ClassLinker> linker(ClassLinker::Create());
+  linker->AppendToClassPath(dex.get());
+  Class* klass = linker->FindClass("LMyClass;", NULL);
+  Method* method = klass->FindDirectMethod("fooSSIOO");
+
+  Assembler jni_asm;
+  JniCompiler jni_compiler;
+  jni_compiler.Compile(&jni_asm, method);
+
+  // TODO: should really use JNIEnv to RegisterNative, but missing a
+  // complete story on this, so hack the RegisterNative below
+  method->RegisterNative(reinterpret_cast<void*>(&Java_MyClass_fooSSIOO));
+
+  jvalue a, b, c, d;
+  a.i = 0;
+  b.l = (jobject)NULL;
+  c.l = (jobject)NULL;
+  EXPECT_EQ(0, gJava_MyClass_fooSSIOO_calls);
+  d = RunMethod(method, a, b, c, a);
+  ASSERT_EQ((jobject)method->GetClass(), d.l);
+  EXPECT_EQ(1, gJava_MyClass_fooSSIOO_calls);
+  a.i = 0;
+  b.l = (jobject)NULL;
+  c.l = (jobject)16;
+  d = RunMethod(method, a, b, c, a);
+  ASSERT_EQ((jobject)method->GetClass(), d.l);
+  EXPECT_EQ(2, gJava_MyClass_fooSSIOO_calls);
+  a.i = 1;
+  d = RunMethod(method, a, b, c, a);
+  ASSERT_EQ((jobject)NULL, d.l);
+  EXPECT_EQ(3, gJava_MyClass_fooSSIOO_calls);
+  a.i = 2;
+  d = RunMethod(method, a, b, c, a);
+  ASSERT_EQ((jobject)16, d.l);
+  EXPECT_EQ(4, gJava_MyClass_fooSSIOO_calls);
+  a.i = 0;
+  b.l = (jobject)16;
+  c.l = (jobject)NULL;
+  d = RunMethod(method, a, b, c, a);
+  ASSERT_EQ((jobject)method->GetClass(), d.l);
+  EXPECT_EQ(5, gJava_MyClass_fooSSIOO_calls);
+  a.i = 1;
+  d = RunMethod(method, a, b, c, a);
+  ASSERT_EQ((jobject)16, d.l);
+  EXPECT_EQ(6, gJava_MyClass_fooSSIOO_calls);
+  a.i = 2;
+  d = RunMethod(method, a, b, c, a);
+  ASSERT_EQ((jobject)NULL, d.l);
+  EXPECT_EQ(7, gJava_MyClass_fooSSIOO_calls);
+}
+
 }  // namespace art
diff --git a/src/jni_internal.cc b/src/jni_internal.cc
new file mode 100644
index 0000000..7a5025a
--- /dev/null
+++ b/src/jni_internal.cc
@@ -0,0 +1,21 @@
+// Copyright 2011 Google Inc. All Rights Reserved.
+
+#include "src/jni_internal.h"
+#include "src/logging.h"
+
+namespace art {
+
+static void JniMonitorEnter(JniEnvironment*, jobject) {
+  LOG(WARNING) << "Unimplemented: JNI Monitor Enter";
+}
+
+static void JniMonitorExit(JniEnvironment*, jobject) {
+  LOG(WARNING) << "Unimplemented: JNI Monitor Exit";
+}
+
+JniEnvironment::JniEnvironment() {
+  monitor_enter_ = &JniMonitorEnter;
+  monitor_exit_ = &JniMonitorExit;
+}
+
+}  // namespace art
diff --git a/src/jni_internal.h b/src/jni_internal.h
new file mode 100644
index 0000000..64941cc
--- /dev/null
+++ b/src/jni_internal.h
@@ -0,0 +1,32 @@
+// Copyright 2011 Google Inc. All Rights Reserved.
+
+#ifndef ART_SRC_JNI_INTERNAL_H_
+#define ART_SRC_JNI_INTERNAL_H_
+
+#include "jni.h"
+#include "src/assembler.h"
+#include "src/macros.h"
+
+namespace art {
+
+// TODO: This is a place holder for a true JNIEnv used to provide limited
+// functionality for the JNI compiler
+class JniEnvironment {
+ public:
+  explicit JniEnvironment();
+
+  static Offset MonitorEnterOffset() {
+    return Offset(OFFSETOF_MEMBER(JniEnvironment, monitor_enter_));
+  }
+
+  static Offset MonitorExitOffset() {
+    return Offset(OFFSETOF_MEMBER(JniEnvironment, monitor_exit_));
+  }
+
+ private:
+  void (*monitor_enter_)(JniEnvironment*, jobject);
+  void (*monitor_exit_)(JniEnvironment*, jobject);
+};
+
+}  // namespace art
+#endif  // ART_SRC_JNI_INTERNAL_H_
diff --git a/src/object.cc b/src/object.cc
index 95e8b67..c8bd353 100644
--- a/src/object.cc
+++ b/src/object.cc
@@ -1,8 +1,8 @@
 // Copyright 2011 Google Inc. All Rights Reserved.
 
 #include "src/object.h"
-#include <algorithm>
 #include <string.h>
+#include <algorithm>
 #include "src/globals.h"
 #include "src/logging.h"
 #include "src/dex_file.h"
@@ -127,14 +127,8 @@
   return (shorty_[param] == 'J') || (shorty_[param] == 'D');
 }
 
-size_t Method::ParamSizeInBytes(unsigned int param) const {
-  CHECK_LT(param, NumArgs());
-  if (IsStatic()) {
-    param++;  // 0th argument must skip return value at start of the shorty
-  } else if (param == 0) {
-    return kPointerSize;  // this argument
-  }
-  switch (shorty_[param]) {
+static size_t ShortyCharToSize(char x) {
+  switch (x) {
     case '[': return kPointerSize;
     case 'L': return kPointerSize;
     case 'D': return 8;
@@ -143,6 +137,20 @@
   }
 }
 
+size_t Method::ParamSize(unsigned int param) const {
+  CHECK_LT(param, NumArgs());
+  if (IsStatic()) {
+    param++;  // 0th argument must skip return value at start of the shorty
+  } else if (param == 0) {
+    return kPointerSize;  // this argument
+  }
+  return ShortyCharToSize(shorty_[param]);
+}
+
+size_t Method::ReturnSize() const {
+  return ShortyCharToSize(shorty_[0]);
+}
+
 bool Method::HasSameArgumentTypes(const Method* that) const {
   const RawDexFile* raw1 = this->GetClass()->GetDexFile()->GetRaw();
   const RawDexFile::ProtoId& proto1 = raw1->GetProtoId(this->proto_idx_);
diff --git a/src/object.h b/src/object.h
index 31d4390..49940e0 100644
--- a/src/object.h
+++ b/src/object.h
@@ -436,7 +436,11 @@
   // Is the given method parameter a long or double?
   bool IsParamALongOrDouble(unsigned int param) const;
 
-  size_t ParamSizeInBytes(unsigned int param) const;
+  // Size in bytes of the given parameter
+  size_t ParamSize(unsigned int param) const;
+
+  // Size in bytes of the return value
+  size_t ReturnSize() const;
 
   void SetCode(const void* code) {
     code_ = code;
diff --git a/src/thread.h b/src/thread.h
index ab0bacc..3f962d5 100644
--- a/src/thread.h
+++ b/src/thread.h
@@ -9,6 +9,7 @@
 
 #include "src/globals.h"
 #include "src/heap.h"
+#include "src/jni_internal.h"
 #include "src/logging.h"
 #include "src/macros.h"
 #include "src/runtime.h"
@@ -179,7 +180,7 @@
   }
 
   // JNI methods
-  JNIEnv* GetJniEnv() const {
+  JniEnvironment* GetJniEnv() const {
     return jni_env_;
   }
 
@@ -204,10 +205,12 @@
 
  private:
   Thread() :
-    thread_id_(1234), top_shb_(NULL),
-    jni_env_(reinterpret_cast<JNIEnv*>(0xEBADC0DE)), exception_(NULL) {
+    thread_id_(1234), top_shb_(NULL), exception_(NULL) {
+    jni_env_ = new JniEnvironment();
   }
-  ~Thread() {}
+  ~Thread() {
+    delete jni_env_;
+  }
 
   void InitCpu();
 
@@ -224,7 +227,7 @@
   StackHandleBlock* top_shb_;
 
   // Every thread may have an associated JNI environment
-  JNIEnv* jni_env_;
+  JniEnvironment* jni_env_;
 
   State state_;