xref: /dalvik/vm/Jni.cpp

/*
 * 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.
 */

/*
 * Dalvik implementation of JNI interfaces.
 */
#include "Dalvik.h"
#include "JniInternal.h"
#include "ScopedPthreadMutexLock.h"
#include "UniquePtr.h"

#include <stdlib.h>
#include <stdarg.h>
#include <limits.h>

/*
Native methods and interaction with the GC

All JNI methods must start by changing their thread status to
THREAD_RUNNING, and finish by changing it back to THREAD_NATIVE before
returning to native code.  The switch to "running" triggers a thread
suspension check.

With a rudimentary GC we should be able to skip the status change for
simple functions, e.g.  IsSameObject, GetJavaVM, GetStringLength, maybe
even access to fields with primitive types.  Our options are more limited
with a compacting GC.

For performance reasons we do as little error-checking as possible here.
For example, we don't check to make sure the correct type of Object is
passed in when setting a field, and we don't prevent you from storing
new values in a "final" field.  Such things are best handled in the
"check" version.  For actions that are common, dangerous, and must be
checked at runtime, such as array bounds checks, we do the tests here.


General notes on local/global reference tracking

JNI provides explicit control over natively-held references that the GC
needs to know about.  These can be local, in which case they're released
when the native method returns into the VM, or global, which are held
until explicitly released.  (There are also weak-global references,
which have the lifespan and visibility of global references, but the
object they refer to may be collected.)

The references can be created with explicit JNI NewLocalRef / NewGlobalRef
calls.  The former is very unusual, the latter is reasonably common
(e.g. for caching references to class objects).

Local references are most often created as a side-effect of JNI functions.
For example, the AllocObject/NewObject functions must create local
references to the objects returned, because nothing else in the GC root
set has a reference to the new objects.

The most common mode of operation is for a method to create zero or
more local references and return.  Explicit "local delete" operations
are expected to be exceedingly rare, except when walking through an
object array, and the Push/PopLocalFrame calls are expected to be used
infrequently.  For efficient operation, we want to add new local refs
with a simple store/increment operation; to avoid infinite growth in
pathological situations, we need to reclaim the space used by deleted
entries.

If we just want to maintain a list for the GC root set, we can use an
expanding append-only array that compacts when objects are deleted.
In typical situations, e.g. running through an array of objects, we will
be deleting one of the most recently added entries, so we can minimize
the number of elements moved (or avoid having to move any).

If we want to conceal the pointer values from native code, which is
necessary to allow the GC to move JNI-referenced objects around, then we
have to use a more complicated indirection mechanism.

The spec says, "Local references are only valid in the thread in which
they are created.  The native code must not pass local references from
one thread to another."


Pinned objects

For some large chunks of data, notably primitive arrays and String data,
JNI allows the VM to choose whether it wants to pin the array object or
make a copy.  We currently pin the memory for better execution performance.

TODO: we're using simple root set references to pin primitive array data,
because they have the property we need (i.e. the pointer we return is
guaranteed valid until we explicitly release it).  However, if we have a
compacting GC and don't want to pin all memory held by all global refs,
we need to treat these differently.


Global reference tracking

There should be a small "active" set centered around the most-recently
added items.

Because it's global, access to it has to be synchronized.  Additions and
removals require grabbing a mutex.  If the table serves as an indirection
mechanism (i.e. it's not just a list for the benefit of the garbage
collector), reference lookups may also require grabbing a mutex.

The JNI spec does not define any sort of limit, so the list must be able
to expand to a reasonable size.  It may be useful to log significant
increases in usage to help identify resource leaks.


Weak-global reference tracking

[TBD]


Local reference tracking

Each Thread/JNIEnv points to an IndirectRefTable.

We implement Push/PopLocalFrame with actual stack frames.  Before a JNI
frame gets popped, we set "nextEntry" to the "top" pointer of the current
frame, effectively releasing the references.

The GC will scan all references in the table.

*/

#ifdef WITH_JNI_STACK_CHECK
# define COMPUTE_STACK_SUM(_self)   computeStackSum(_self);
# define CHECK_STACK_SUM(_self)     checkStackSum(_self);

/*
 * Compute a CRC on the entire interpreted stack.
 *
 * Would be nice to compute it on "self" as well, but there are parts of
 * the Thread that can be altered by other threads (e.g. prev/next pointers).
 */
static void computeStackSum(Thread* self) {
    const u1* low = (const u1*)SAVEAREA_FROM_FP(self->interpSave.curFrame);
    u4 crc = dvmInitCrc32();
    self->stackCrc = 0;
    crc = dvmComputeCrc32(crc, low, self->interpStackStart - low);
    self->stackCrc = crc;
}

/*
 * Compute a CRC on the entire interpreted stack, and compare it to what
 * we previously computed.
 *
 * We can execute JNI directly from native code without calling in from
 * interpreted code during VM initialization and immediately after JNI
 * thread attachment.  Another opportunity exists during JNI_OnLoad.  Rather
 * than catching these cases we just ignore them here, which is marginally
 * less accurate but reduces the amount of code we have to touch with #ifdefs.
 */
static void checkStackSum(Thread* self) {
    const u1* low = (const u1*)SAVEAREA_FROM_FP(self->interpSave.curFrame);
    u4 stackCrc = self->stackCrc;
    self->stackCrc = 0;
    u4 crc = dvmInitCrc32();
    crc = dvmComputeCrc32(crc, low, self->interpStackStart - low);
    if (crc != stackCrc) {
        const Method* meth = dvmGetCurrentJNIMethod();
        if (dvmComputeExactFrameDepth(self->interpSave.curFrame) == 1) {
            LOGD("JNI: bad stack CRC (0x%08x) -- okay during init", stackCrc);
        } else if (strcmp(meth->name, "nativeLoad") == 0 &&
                (strcmp(meth->clazz->descriptor, "Ljava/lang/Runtime;") == 0)) {
            LOGD("JNI: bad stack CRC (0x%08x) -- okay during JNI_OnLoad", stackCrc);
        } else {
            LOGW("JNI: bad stack CRC (%08x vs %08x)", crc, stackCrc);
            dvmAbort();
        }
    }
    self->stackCrc = (u4) -1;       /* make logic errors more noticeable */
}

#else
# define COMPUTE_STACK_SUM(_self)   ((void)0)
# define CHECK_STACK_SUM(_self)     ((void)0)
#endif


/*
 * ===========================================================================
 *      Utility functions
 * ===========================================================================
 */

static inline Thread* self(JNIEnv* env) {
    Thread* envSelf = ((JNIEnvExt*) env)->self;
    // When emulating direct pointers with indirect references, it's critical
    // that we use the correct per-thread indirect reference table.
    Thread* self = gDvmJni.workAroundAppJniBugs ? dvmThreadSelf() : envSelf;
    if (self != envSelf) {
        LOGE("JNI ERROR: env->self != thread-self (%p vs. %p); auto-correcting",
                envSelf, self);
    }
    return self;
}

/*
 * Entry/exit processing for all JNI calls.
 *
 * We skip the (curiously expensive) thread-local storage lookup on our Thread*.
 * If the caller has passed the wrong JNIEnv in, we're going to be accessing unsynchronized
 * structures from more than one thread, and things are going to fail
 * in bizarre ways.  This is only sensible if the native code has been
 * fully exercised with CheckJNI enabled.
 */
class ScopedJniThreadState {
public:
    explicit ScopedJniThreadState(JNIEnv* env) {
        mSelf = ::self(env);
        CHECK_STACK_SUM(mSelf);
        dvmChangeStatus(mSelf, THREAD_RUNNING);
    }

    ~ScopedJniThreadState() {
        dvmChangeStatus(mSelf, THREAD_NATIVE);
        COMPUTE_STACK_SUM(mSelf);
    }

    Thread* self() {
        return mSelf;
    }

private:
    Thread* mSelf;

    // Disallow copy and assignment.
    ScopedJniThreadState(const ScopedJniThreadState&);
    void operator=(const ScopedJniThreadState&);
};

#define kGlobalRefsTableInitialSize 512
#define kGlobalRefsTableMaxSize     51200       /* arbitrary, must be < 64K */
#define kGrefWaterInterval          100
#define kTrackGrefUsage             true

#define kWeakGlobalRefsTableInitialSize 16

#define kPinTableInitialSize        16
#define kPinTableMaxSize            1024
#define kPinComplainThreshold       10

bool dvmJniStartup() {
    if (!gDvm.jniGlobalRefTable.init(kGlobalRefsTableInitialSize,
                                 kGlobalRefsTableMaxSize,
                                 kIndirectKindGlobal)) {
        return false;
    }
    if (!gDvm.jniWeakGlobalRefTable.init(kWeakGlobalRefsTableInitialSize,
                                 kGlobalRefsTableMaxSize,
                                 kIndirectKindWeakGlobal)) {
        return false;
    }

    dvmInitMutex(&gDvm.jniGlobalRefLock);
    dvmInitMutex(&gDvm.jniWeakGlobalRefLock);
    gDvm.jniGlobalRefLoMark = 0;
    gDvm.jniGlobalRefHiMark = kGrefWaterInterval * 2;

    if (!dvmInitReferenceTable(&gDvm.jniPinRefTable, kPinTableInitialSize, kPinTableMaxSize)) {
        return false;
    }

    dvmInitMutex(&gDvm.jniPinRefLock);

    return true;
}

void dvmJniShutdown() {
    gDvm.jniGlobalRefTable.destroy();
    gDvm.jniWeakGlobalRefTable.destroy();
    dvmClearReferenceTable(&gDvm.jniPinRefTable);
}

/*
 * Find the JNIEnv associated with the current thread.
 *
 * Currently stored in the Thread struct.  Could also just drop this into
 * thread-local storage.
 */
JNIEnvExt* dvmGetJNIEnvForThread() {
    Thread* self = dvmThreadSelf();
    if (self == NULL) {
        return NULL;
    }
    return (JNIEnvExt*) dvmGetThreadJNIEnv(self);
}

/*
 * Retrieve the ReferenceTable struct for the current thread.
 *
 * Going through "env" rather than dvmThreadSelf() is faster but will
 * get weird if the JNI code is passing the wrong JNIEnv around.
 */
static inline IndirectRefTable* getLocalRefTable(JNIEnv* env) {
    return &self(env)->jniLocalRefTable;
}

/*
 * Convert an indirect reference to an Object reference.  The indirect
 * reference may be local, global, or weak-global.
 *
 * If "jobj" is NULL, or is a weak global reference whose reference has
 * been cleared, this returns NULL.  If jobj is an invalid indirect
 * reference, kInvalidIndirectRefObject is returned.
 *
 * Note "env" may be NULL when decoding global references.
 */
Object* dvmDecodeIndirectRef(JNIEnv* env, jobject jobj) {
    if (jobj == NULL) {
        return NULL;
    }

    switch (indirectRefKind(jobj)) {
    case kIndirectKindLocal:
        {
            Object* result = getLocalRefTable(env)->get(jobj);
            if (result == NULL) {
                LOGE("JNI ERROR (app bug): use of deleted local reference (%p)", jobj);
                dvmAbort();
            }
            return result;
        }
    case kIndirectKindGlobal:
        {
            // TODO: find a way to avoid the mutex activity here
            IndirectRefTable* pRefTable = &gDvm.jniGlobalRefTable;
            ScopedPthreadMutexLock lock(&gDvm.jniGlobalRefLock);
            Object* result = pRefTable->get(jobj);
            if (result == NULL) {
                LOGE("JNI ERROR (app bug): use of deleted global reference (%p)", jobj);
                dvmAbort();
            }
            return result;
        }
    case kIndirectKindWeakGlobal:
        {
            // TODO: find a way to avoid the mutex activity here
            IndirectRefTable* pRefTable = &gDvm.jniWeakGlobalRefTable;
            ScopedPthreadMutexLock lock(&gDvm.jniWeakGlobalRefLock);
            Object* result = pRefTable->get(jobj);
            // There's no null check here because we might be dealing with
            // a cleared weak global reference.
            /*
             * TODO: this is a temporary workaround for broken weak global
             * refs (http://b/4260055).  We treat any invalid reference as if it
             * were a weak global with a cleared referent.  This means that
             * actual invalid references won't be detected, and if an empty
             * slot gets re-used we will return the new reference instead.
             * This must be removed when weak global refs get fixed.
             */
            if (result == kInvalidIndirectRefObject) {
                LOGW("Warning: used weak global ref hack");
                result = NULL;
            }
            return result;
        }
    case kIndirectKindInvalid:
    default:
        if (gDvmJni.workAroundAppJniBugs) {
            // Assume an invalid local reference is actually a direct pointer.
            return reinterpret_cast<Object*>(jobj);
        }
        LOGW("Invalid indirect reference %p in decodeIndirectRef", jobj);
        dvmAbort();
        return kInvalidIndirectRefObject;
    }
}

/*
 * Add a local reference for an object to the current stack frame.  When
 * the native function returns, the reference will be discarded.
 *
 * We need to allow the same reference to be added multiple times.
 *
 * This will be called on otherwise unreferenced objects.  We cannot do
 * GC allocations here, and it's best if we don't grab a mutex.
 *
 * Returns the local reference (currently just the same pointer that was
 * passed in), or NULL on failure.
 */
static jobject addLocalReference(JNIEnv* env, Object* obj) {
    if (obj == NULL) {
        return NULL;
    }

    IndirectRefTable* pRefTable = getLocalRefTable(env);
    void* curFrame = self(env)->interpSave.curFrame;
    u4 cookie = SAVEAREA_FROM_FP(curFrame)->xtra.localRefCookie;
    jobject jobj = (jobject) pRefTable->add(cookie, obj);
    if (jobj == NULL) {
        pRefTable->dump("JNI local");
        LOGE("Failed adding to JNI local ref table (has %zd entries)",
                pRefTable->capacity());
        dvmDumpThread(dvmThreadSelf(), false);
        dvmAbort();     // spec says call FatalError; this is equivalent
    } else {
        if (false) {
            LOGI("LREF add %p  (%s.%s) (ent=%zd)", obj,
                    dvmGetCurrentJNIMethod()->clazz->descriptor,
                    dvmGetCurrentJNIMethod()->name,
                    pRefTable->capacity());
        }
    }

#if 0 // TODO: fix this to understand PushLocalFrame, so we can turn it on.
    if (gDvmJni.useCheckJni) {
        size_t entryCount = pRefTable->capacity();
        if (entryCount > 16) {
            LOGW("Warning: more than 16 JNI local references: %d (most recent was a %s)", entryCount, obj->clazz->descriptor);
            pRefTable->dump("JNI local");
            dvmDumpThread(dvmThreadSelf(), false);
            //dvmAbort();
        }
    }
#endif

    if (gDvmJni.workAroundAppJniBugs) {
        // Hand out direct pointers to support broken old apps.
        return reinterpret_cast<jobject>(obj);
    }
    return jobj;
}

/*
 * Ensure that at least "capacity" references can be held in the local
 * refs table of the current thread.
 */
static bool ensureLocalCapacity(JNIEnv* env, int capacity) {
    IndirectRefTable* pRefTable = getLocalRefTable(env);
    int numEntries = pRefTable->capacity();
    // TODO: this isn't quite right, since "numEntries" includes holes
    return ((kJniLocalRefMax - numEntries) >= capacity);
}

/*
 * Explicitly delete a reference from the local list.
 */
static void deleteLocalReference(JNIEnv* env, jobject jobj) {
    if (jobj == NULL) {
        return;
    }

    IndirectRefTable* pRefTable = getLocalRefTable(env);
    void* curFrame = self(env)->interpSave.curFrame;
    u4 cookie = SAVEAREA_FROM_FP(curFrame)->xtra.localRefCookie;
    if (!pRefTable->remove(cookie, jobj)) {
        /*
         * Attempting to delete a local reference that is not in the
         * topmost local reference frame is a no-op.  DeleteLocalRef returns
         * void and doesn't throw any exceptions, but we should probably
         * complain about it so the user will notice that things aren't
         * going quite the way they expect.
         */
        LOGW("JNI WARNING: DeleteLocalRef(%p) failed to find entry", jobj);
    }
}

/*
 * Add a global reference for an object.
 *
 * We may add the same object more than once.  Add/remove calls are paired,
 * so it needs to appear on the list multiple times.
 */
static jobject addGlobalReference(Object* obj) {
    if (obj == NULL) {
        return NULL;
    }

    //LOGI("adding obj=%p", obj);
    //dvmDumpThread(dvmThreadSelf(), false);

    if (false && dvmIsClassObject((Object*)obj)) {
        ClassObject* clazz = (ClassObject*) obj;
        LOGI("-------");
        LOGI("Adding global ref on class %s", clazz->descriptor);
        dvmDumpThread(dvmThreadSelf(), false);
    }
    if (false && ((Object*)obj)->clazz == gDvm.classJavaLangString) {
        StringObject* strObj = (StringObject*) obj;
        char* str = dvmCreateCstrFromString(strObj);
        if (strcmp(str, "sync-response") == 0) {
            LOGI("-------");
            LOGI("Adding global ref on string '%s'", str);
            dvmDumpThread(dvmThreadSelf(), false);
            //dvmAbort();
        }
        free(str);
    }
    if (false && ((Object*)obj)->clazz == gDvm.classArrayByte) {
        ArrayObject* arrayObj = (ArrayObject*) obj;
        if (arrayObj->length == 8192 /*&&
            dvmReferenceTableEntries(&gDvm.jniGlobalRefTable) > 400*/)
        {
            LOGI("Adding global ref on byte array %p (len=%d)",
                arrayObj, arrayObj->length);
            dvmDumpThread(dvmThreadSelf(), false);
        }
    }

    ScopedPthreadMutexLock lock(&gDvm.jniGlobalRefLock);

    /*
     * Throwing an exception on failure is problematic, because JNI code
     * may not be expecting an exception, and things sort of cascade.  We
     * want to have a hard limit to catch leaks during debugging, but this
     * otherwise needs to expand until memory is consumed.  As a practical
     * matter, if we have many thousands of global references, chances are
     * we're either leaking global ref table entries or we're going to
     * run out of space in the GC heap.
     */
    jobject jobj = (jobject) gDvm.jniGlobalRefTable.add(IRT_FIRST_SEGMENT, obj);
    if (jobj == NULL) {
        gDvm.jniGlobalRefTable.dump("JNI global");
        LOGE("Failed adding to JNI global ref table (%zd entries)",
                gDvm.jniGlobalRefTable.capacity());
        dvmAbort();
    }

    LOGVV("GREF add %p  (%s.%s)", obj,
        dvmGetCurrentJNIMethod()->clazz->descriptor,
        dvmGetCurrentJNIMethod()->name);

    /* GREF usage tracking; should probably be disabled for production env */
    if (kTrackGrefUsage && gDvm.jniGrefLimit != 0) {
        int count = gDvm.jniGlobalRefTable.capacity();
        // TODO: adjust for "holes"
        if (count > gDvm.jniGlobalRefHiMark) {
            LOGD("GREF has increased to %d", count);
            gDvm.jniGlobalRefHiMark += kGrefWaterInterval;
            gDvm.jniGlobalRefLoMark += kGrefWaterInterval;

            /* watch for "excessive" use; not generally appropriate */
            if (count >= gDvm.jniGrefLimit) {
                if (gDvmJni.warnOnly) {
                    LOGW("Excessive JNI global references (%d)", count);
                } else {
                    gDvm.jniGlobalRefTable.dump("JNI global");
                    LOGE("Excessive JNI global references (%d)", count);
                    dvmAbort();
                }
            }
        }
    }
    return jobj;
}

static jobject addWeakGlobalReference(Object* obj) {
    if (obj == NULL) {
        return NULL;
    }

    ScopedPthreadMutexLock lock(&gDvm.jniWeakGlobalRefLock);
    IndirectRefTable *table = &gDvm.jniWeakGlobalRefTable;
    jobject jobj = (jobject) table->add(IRT_FIRST_SEGMENT, obj);
    if (jobj == NULL) {
        table->dump("JNI weak global");
        LOGE("Failed adding to JNI weak global ref table (%zd entries)",
                table->capacity());
    }
    return jobj;
}

static void deleteWeakGlobalReference(jobject jobj) {
    if (jobj == NULL) {
        return;
    }

    ScopedPthreadMutexLock lock(&gDvm.jniWeakGlobalRefLock);
    IndirectRefTable *table = &gDvm.jniWeakGlobalRefTable;
    if (!table->remove(IRT_FIRST_SEGMENT, jobj)) {
        LOGW("JNI: DeleteWeakGlobalRef(%p) failed to find entry", jobj);
    }
}

/*
 * Remove a global reference.  In most cases it's the entry most recently
 * added, which makes this pretty quick.
 *
 * Thought: if it's not the most recent entry, just null it out.  When we
 * fill up, do a compaction pass before we expand the list.
 */
static void deleteGlobalReference(jobject jobj) {
    if (jobj == NULL) {
        return;
    }

    ScopedPthreadMutexLock lock(&gDvm.jniGlobalRefLock);
    if (!gDvm.jniGlobalRefTable.remove(IRT_FIRST_SEGMENT, jobj)) {
        LOGW("JNI: DeleteGlobalRef(%p) failed to find entry", jobj);
        return;
    }

    if (kTrackGrefUsage && gDvm.jniGrefLimit != 0) {
        int count = gDvm.jniGlobalRefTable.capacity();
        // TODO: not quite right, need to subtract holes
        if (count < gDvm.jniGlobalRefLoMark) {
            LOGD("GREF has decreased to %d", count);
            gDvm.jniGlobalRefHiMark -= kGrefWaterInterval;
            gDvm.jniGlobalRefLoMark -= kGrefWaterInterval;
        }
    }
}

/*
 * Objects don't currently move, so we just need to create a reference
 * that will ensure the array object isn't collected.
 *
 * We use a separate reference table, which is part of the GC root set.
 */
static void pinPrimitiveArray(ArrayObject* arrayObj) {
    if (arrayObj == NULL) {
        return;
    }

    ScopedPthreadMutexLock lock(&gDvm.jniPinRefLock);

    if (!dvmAddToReferenceTable(&gDvm.jniPinRefTable, (Object*)arrayObj)) {
        dvmDumpReferenceTable(&gDvm.jniPinRefTable, "JNI pinned array");
        LOGE("Failed adding to JNI pinned array ref table (%d entries)",
           (int) dvmReferenceTableEntries(&gDvm.jniPinRefTable));
        dvmDumpThread(dvmThreadSelf(), false);
        dvmAbort();
    }

    /*
     * If we're watching global ref usage, also keep an eye on these.
     *
     * The total number of pinned primitive arrays should be pretty small.
     * A single array should not be pinned more than once or twice; any
     * more than that is a strong indicator that a Release function is
     * not being called.
     */
    if (kTrackGrefUsage && gDvm.jniGrefLimit != 0) {
        int count = 0;
        Object** ppObj = gDvm.jniPinRefTable.table;
        while (ppObj < gDvm.jniPinRefTable.nextEntry) {
            if (*ppObj++ == (Object*) arrayObj)
                count++;
        }

        if (count > kPinComplainThreshold) {
            LOGW("JNI: pin count on array %p (%s) is now %d",
                arrayObj, arrayObj->clazz->descriptor, count);
            /* keep going */
        }
    }
}

/*
 * Un-pin the array object.  If an object was pinned twice, it must be
 * unpinned twice before it's free to move.
 */
static void unpinPrimitiveArray(ArrayObject* arrayObj) {
    if (arrayObj == NULL) {
        return;
    }

    ScopedPthreadMutexLock lock(&gDvm.jniPinRefLock);
    if (!dvmRemoveFromReferenceTable(&gDvm.jniPinRefTable,
            gDvm.jniPinRefTable.table, (Object*) arrayObj))
    {
        LOGW("JNI: unpinPrimitiveArray(%p) failed to find entry (valid=%d)",
            arrayObj, dvmIsValidObject((Object*) arrayObj));
        return;
    }
}

/*
 * Dump the contents of the JNI reference tables to the log file.
 *
 * We only dump the local refs associated with the current thread.
 */
void dvmDumpJniReferenceTables() {
    Thread* self = dvmThreadSelf();
    JNIEnv* env = self->jniEnv;
    IndirectRefTable* pLocalRefs = getLocalRefTable(env);
    pLocalRefs->dump("JNI local");
    gDvm.jniGlobalRefTable.dump("JNI global");
    dvmDumpReferenceTable(&gDvm.jniPinRefTable, "JNI pinned array");
}

/*
 * Verify that a reference passed in from native code is one that the
 * code is allowed to have.
 *
 * It's okay for native code to pass us a reference that:
 *  - was passed in as an argument when invoked by native code (and hence
 *    is in the JNI local refs table)
 *  - was returned to it from JNI (and is now in the local refs table)
 *  - is present in the JNI global refs table
 *
 * Used by -Xcheck:jni and GetObjectRefType.
 */
jobjectRefType dvmGetJNIRefType(JNIEnv* env, jobject jobj) {
    /*
     * IndirectRefKind is currently defined as an exact match of
     * jobjectRefType, so this is easy.  We have to decode it to determine
     * if it's a valid reference and not merely valid-looking.
     */
    assert(jobj != NULL);

    Object* obj = dvmDecodeIndirectRef(env, jobj);
    if (obj == reinterpret_cast<Object*>(jobj) && gDvmJni.workAroundAppJniBugs) {
        // If we're handing out direct pointers, check whether 'jobj' is a direct reference
        // to a local reference.
        return getLocalRefTable(env)->contains(jobj) ? JNILocalRefType : JNIInvalidRefType;
    } else if (obj == kInvalidIndirectRefObject) {
        return JNIInvalidRefType;
    } else {
        return (jobjectRefType) indirectRefKind(jobj);
    }
}

static void dumpMethods(Method* methods, size_t methodCount, const char* name) {
    size_t i;
    for (i = 0; i < methodCount; ++i) {
        Method* method = &methods[i];
        if (strcmp(name, method->name) == 0) {
            char* desc = dexProtoCopyMethodDescriptor(&method->prototype);
            LOGE("Candidate: %s.%s:%s", method->clazz->descriptor, name, desc);
            free(desc);
        }
    }
}

static void dumpCandidateMethods(ClassObject* clazz, const char* methodName, const char* signature) {
    LOGE("ERROR: couldn't find native method");
    LOGE("Requested: %s.%s:%s", clazz->descriptor, methodName, signature);
    dumpMethods(clazz->virtualMethods, clazz->virtualMethodCount, methodName);
    dumpMethods(clazz->directMethods, clazz->directMethodCount, methodName);
}

/*
 * Register a method that uses JNI calling conventions.
 */
static bool dvmRegisterJNIMethod(ClassObject* clazz, const char* methodName,
    const char* signature, void* fnPtr)
{
    if (fnPtr == NULL) {
        return false;
    }

    // If a signature starts with a '!', we take that as a sign that the native code doesn't
    // need the extra JNI arguments (the JNIEnv* and the jclass).
    bool fastJni = false;
    if (*signature == '!') {
        fastJni = true;
        ++signature;
        LOGV("fast JNI method %s.%s:%s detected", clazz->descriptor, methodName, signature);
    }

    Method* method = dvmFindDirectMethodByDescriptor(clazz, methodName, signature);
    if (method == NULL) {
        method = dvmFindVirtualMethodByDescriptor(clazz, methodName, signature);
    }
    if (method == NULL) {
        dumpCandidateMethods(clazz, methodName, signature);
        return false;
    }

    if (!dvmIsNativeMethod(method)) {
        LOGW("Unable to register: not native: %s.%s:%s", clazz->descriptor, methodName, signature);
        return false;
    }

    if (fastJni) {
        // In this case, we have extra constraints to check...
        if (dvmIsSynchronizedMethod(method)) {
            // Synchronization is usually provided by the JNI bridge,
            // but we won't have one.
            LOGE("fast JNI method %s.%s:%s cannot be synchronized",
                    clazz->descriptor, methodName, signature);
            return false;
        }
        if (!dvmIsStaticMethod(method)) {
            // There's no real reason for this constraint, but since we won't
            // be supplying a JNIEnv* or a jobject 'this', you're effectively
            // static anyway, so it seems clearer to say so.
            LOGE("fast JNI method %s.%s:%s cannot be non-static",
                    clazz->descriptor, methodName, signature);
            return false;
        }
    }

    if (method->nativeFunc != dvmResolveNativeMethod) {
        /* this is allowed, but unusual */
        LOGV("Note: %s.%s:%s was already registered", clazz->descriptor, methodName, signature);
    }

    method->fastJni = fastJni;
    dvmUseJNIBridge(method, fnPtr);

    LOGV("JNI-registered %s.%s:%s", clazz->descriptor, methodName, signature);
    return true;
}

static const char* builtInPrefixes[] = {
    "Landroid/",
    "Lcom/android/",
    "Lcom/google/android/",
    "Ldalvik/",
    "Ljava/",
    "Ljavax/",
    "Llibcore/",
    "Lorg/apache/harmony/",
};

static bool shouldTrace(Method* method) {
    const char* className = method->clazz->descriptor;
    // Return true if the -Xjnitrace setting implies we should trace 'method'.
    if (gDvm.jniTrace && strstr(className, gDvm.jniTrace)) {
        return true;
    }
    // Return true if we're trying to log all third-party JNI activity and 'method' doesn't look
    // like part of Android.
    if (gDvmJni.logThirdPartyJni) {
        for (size_t i = 0; i < NELEM(builtInPrefixes); ++i) {
            if (strstr(className, builtInPrefixes[i]) == className) {
                return false;
            }
        }
        return true;
    }
    return false;
}

/*
 * Point "method->nativeFunc" at the JNI bridge, and overload "method->insns"
 * to point at the actual function.
 */
void dvmUseJNIBridge(Method* method, void* func) {
    method->shouldTrace = shouldTrace(method);

    // Does the method take any reference arguments?
    method->noRef = true;
    const char* cp = method->shorty;
    while (*++cp != '\0') { // Pre-increment to skip return type.
        if (*cp == 'L') {
            method->noRef = false;
            break;
        }
    }

    DalvikBridgeFunc bridge = gDvmJni.useCheckJni ? dvmCheckCallJNIMethod : dvmCallJNIMethod;
    dvmSetNativeFunc(method, bridge, (const u2*) func);
}

// TODO: rewrite this to share code with CheckJNI's tracing...
static void appendValue(char type, const JValue value, char* buf, size_t n, bool appendComma)
{
    size_t len = strlen(buf);
    if (len >= n - 32) { // 32 should be longer than anything we could append.
        buf[len - 1] = '.';
        buf[len - 2] = '.';
        buf[len - 3] = '.';
        return;
    }
    char* p = buf + len;
    switch (type) {
    case 'B':
        if (value.b >= 0 && value.b < 10) {
            sprintf(p, "%d", value.b);
        } else {
            sprintf(p, "%#x (%d)", value.b, value.b);
        }
        break;
    case 'C':
        if (value.c < 0x7f && value.c >= ' ') {
            sprintf(p, "U+%x ('%c')", value.c, value.c);
        } else {
            sprintf(p, "U+%x", value.c);
        }
        break;
    case 'D':
        sprintf(p, "%g", value.d);
        break;
    case 'F':
        sprintf(p, "%g", value.f);
        break;
    case 'I':
        sprintf(p, "%d", value.i);
        break;
    case 'L':
        sprintf(p, "%#x", value.i);
        break;
    case 'J':
        sprintf(p, "%lld", value.j);
        break;
    case 'S':
        sprintf(p, "%d", value.s);
        break;
    case 'V':
        strcpy(p, "void");
        break;
    case 'Z':
        strcpy(p, value.z ? "true" : "false");
        break;
    default:
        sprintf(p, "unknown type '%c'", type);
        break;
    }

    if (appendComma) {
        strcat(p, ", ");
    }
}

static void logNativeMethodEntry(const Method* method, const u4* args)
{
    char thisString[32] = { 0 };
    const u4* sp = args;
    if (!dvmIsStaticMethod(method)) {
        sprintf(thisString, "this=0x%08x ", *sp++);
    }

    char argsString[128]= { 0 };
    const char* desc = &method->shorty[1];
    while (*desc != '\0') {
        char argType = *desc++;
        JValue value;
        if (argType == 'D' || argType == 'J') {
            value.j = dvmGetArgLong(sp, 0);
            sp += 2;
        } else {
            value.i = *sp++;
        }
        appendValue(argType, value, argsString, sizeof(argsString),
        *desc != '\0');
    }

    std::string className(dvmHumanReadableDescriptor(method->clazz->descriptor));
    char* signature = dexProtoCopyMethodDescriptor(&method->prototype);
    LOGI("-> %s %s%s %s(%s)", className.c_str(), method->name, signature, thisString, argsString);
    free(signature);
}

static void logNativeMethodExit(const Method* method, Thread* self, const JValue returnValue)
{
    std::string className(dvmHumanReadableDescriptor(method->clazz->descriptor));
    char* signature = dexProtoCopyMethodDescriptor(&method->prototype);
    if (dvmCheckException(self)) {
        Object* exception = dvmGetException(self);
        std::string exceptionClassName(dvmHumanReadableDescriptor(exception->clazz->descriptor));
        LOGI("<- %s %s%s threw %s", className.c_str(),
                method->name, signature, exceptionClassName.c_str());
    } else {
        char returnValueString[128] = { 0 };
        char returnType = method->shorty[0];
        appendValue(returnType, returnValue, returnValueString, sizeof(returnValueString), false);
        LOGI("<- %s %s%s returned %s", className.c_str(),
                method->name, signature, returnValueString);
    }
    free(signature);
}

/*
 * Get the method currently being executed by examining the interp stack.
 */
const Method* dvmGetCurrentJNIMethod() {
    assert(dvmThreadSelf() != NULL);

    void* fp = dvmThreadSelf()->interpSave.curFrame;
    const Method* meth = SAVEAREA_FROM_FP(fp)->method;

    assert(meth != NULL);
    assert(dvmIsNativeMethod(meth));
    return meth;
}

/*
 * Track a JNI MonitorEnter in the current thread.
 *
 * The goal is to be able to "implicitly" release all JNI-held monitors
 * when the thread detaches.
 *
 * Monitors may be entered multiple times, so we add a new entry for each
 * enter call.  It would be more efficient to keep a counter.  At present
 * there's no real motivation to improve this however.
 */
static void trackMonitorEnter(Thread* self, Object* obj) {
    static const int kInitialSize = 16;
    ReferenceTable* refTable = &self->jniMonitorRefTable;

    /* init table on first use */
    if (refTable->table == NULL) {
        assert(refTable->maxEntries == 0);

        if (!dvmInitReferenceTable(refTable, kInitialSize, INT_MAX)) {
            LOGE("Unable to initialize monitor tracking table");
            dvmAbort();
        }
    }

    if (!dvmAddToReferenceTable(refTable, obj)) {
        /* ran out of memory? could throw exception instead */
        LOGE("Unable to add entry to monitor tracking table");
        dvmAbort();
    } else {
        LOGVV("--- added monitor %p", obj);
    }
}

/*
 * Track a JNI MonitorExit in the current thread.
 */
static void trackMonitorExit(Thread* self, Object* obj) {
    ReferenceTable* pRefTable = &self->jniMonitorRefTable;

    if (!dvmRemoveFromReferenceTable(pRefTable, pRefTable->table, obj)) {
        LOGE("JNI monitor %p not found in tracking list", obj);
        /* keep going? */
    } else {
        LOGVV("--- removed monitor %p", obj);
    }
}

/*
 * Release all monitors held by the jniMonitorRefTable list.
 */
void dvmReleaseJniMonitors(Thread* self) {
    ReferenceTable* pRefTable = &self->jniMonitorRefTable;
    Object** top = pRefTable->table;

    if (top == NULL) {
        return;
    }
    Object** ptr = pRefTable->nextEntry;
    while (--ptr >= top) {
        if (!dvmUnlockObject(self, *ptr)) {
            LOGW("Unable to unlock monitor %p at thread detach", *ptr);
        } else {
            LOGVV("--- detach-releasing monitor %p", *ptr);
        }
    }

    /* zap it */
    pRefTable->nextEntry = pRefTable->table;
}

/*
 * Determine if the specified class can be instantiated from JNI.  This
 * is used by AllocObject / NewObject, which are documented as throwing
 * an exception for abstract and interface classes, and not accepting
 * array classes.  We also want to reject attempts to create new Class
 * objects, since only DefineClass should do that.
 */
static bool canAllocClass(ClassObject* clazz) {
    if (dvmIsAbstractClass(clazz) || dvmIsInterfaceClass(clazz)) {
        /* JNI spec defines what this throws */
        dvmThrowInstantiationException(clazz, "abstract class or interface");
        return false;
    } else if (dvmIsArrayClass(clazz) || dvmIsTheClassClass(clazz)) {
        /* spec says "must not" for arrays, ignores Class */
        dvmThrowInstantiationException(clazz, "wrong JNI function");
        return false;
    }
    return true;
}


/*
 * ===========================================================================
 *      JNI call bridge
 * ===========================================================================
 */

/*
 * The functions here form a bridge between interpreted code and JNI native
 * functions.  The basic task is to convert an array of primitives and
 * references into C-style function arguments.  This is architecture-specific
 * and usually requires help from assembly code.
 *
 * The bridge takes four arguments: the array of parameters, a place to
 * store the function result (if any), the method to call, and a pointer
 * to the current thread.
 *
 * These functions aren't called directly from elsewhere in the VM.
 * A pointer in the Method struct points to one of these, and when a native
 * method is invoked the interpreter jumps to it.
 *
 * (The "internal native" methods are invoked the same way, but instead
 * of calling through a bridge, the target method is called directly.)
 *
 * The "args" array should not be modified, but we do so anyway for
 * performance reasons.  We know that it points to the "outs" area on
 * the current method's interpreted stack.  This area is ignored by the
 * precise GC, because there is no register map for a native method (for
 * an interpreted method the args would be listed in the argument set).
 * We know all of the values exist elsewhere on the interpreted stack,
 * because the method call setup copies them right before making the call,
 * so we don't have to worry about concealing stuff from the GC.
 *
 * If we don't want to modify "args", we either have to create a local
 * copy and modify it before calling dvmPlatformInvoke, or we have to do
 * the local reference replacement within dvmPlatformInvoke.  The latter
 * has some performance advantages, though if we can inline the local
 * reference adds we may win when there's a lot of reference args (unless
 * we want to code up some local ref table manipulation in assembly.
 */

/*
 * If necessary, convert the value in pResult from a local/global reference
 * to an object pointer.
 *
 * If the returned reference is invalid, kInvalidIndirectRefObject will
 * be returned in pResult.
 */
static inline void convertReferenceResult(JNIEnv* env, JValue* pResult,
    const Method* method, Thread* self)
{
    if (method->shorty[0] == 'L' && !dvmCheckException(self) && pResult->l != NULL) {
        pResult->l = dvmDecodeIndirectRef(env, (jobject) pResult->l);
    }
}

/*
 * General form, handles all cases.
 */
void dvmCallJNIMethod(const u4* args, JValue* pResult, const Method* method, Thread* self) {
    u4* modArgs = (u4*) args;
    jclass staticMethodClass = NULL;
    JNIEnv* env = self->jniEnv;

    bool isSynchronized = dvmIsSynchronizedMethod(method);
    Object* lockObj;

    //LOGI("JNI calling %p (%s.%s:%s):", method->insns,
    //    method->clazz->descriptor, method->name, method->shorty);

    /*
     * Walk the argument list, creating local references for appropriate
     * arguments.
     */
    int idx = 0;
    if (dvmIsStaticMethod(method)) {
        lockObj = (Object*) method->clazz;

        /* add the class object we pass in */
        staticMethodClass = (jclass) addLocalReference(env, (Object*) method->clazz);
        if (staticMethodClass == NULL) {
            assert(dvmCheckException(self));
            return;
        }
    } else {
        lockObj = (Object*) args[0];

        /* add "this" */
        jobject thisObj = addLocalReference(env, (Object*) modArgs[0]);
        if (thisObj == NULL) {
            assert(dvmCheckException(self));
            return;
        }
        modArgs[idx] = (u4) thisObj;
        idx = 1;
    }

    if (!method->noRef) {
        const char* shorty = &method->shorty[1];        /* skip return type */
        while (*shorty != '\0') {
            switch (*shorty++) {
            case 'L':
                //LOGI("  local %d: 0x%08x", idx, modArgs[idx]);
                if (modArgs[idx] != 0) {
                    //if (!dvmIsValidObject((Object*) modArgs[idx]))
                    //    dvmAbort();
                    jobject argObj = addLocalReference(env, (Object*) modArgs[idx]);
                    if (argObj == NULL) {
                        assert(dvmCheckException(self));
                        return;
                    }
                    modArgs[idx] = (u4) argObj;
                }
                break;
            case 'D':
            case 'J':
                idx++;
                break;
            default:
                /* Z B C S I -- do nothing */
                break;
            }
            idx++;
        }
    }

    if (method->shouldTrace) {
        logNativeMethodEntry(method, args);
    }
    if (isSynchronized) {
        dvmLockObject(self, lockObj);
    }

    ThreadStatus oldStatus = dvmChangeStatus(self, THREAD_NATIVE);

    ANDROID_MEMBAR_FULL();      /* guarantee ordering on method->insns */
    assert(method->insns != NULL);

    COMPUTE_STACK_SUM(self);
    dvmPlatformInvoke(method->fastJni ? NULL : env,
            (ClassObject*) staticMethodClass,
            method->jniArgInfo, method->insSize, modArgs, method->shorty,
            (void*) method->insns, pResult);
    CHECK_STACK_SUM(self);

    dvmChangeStatus(self, oldStatus);

    convertReferenceResult(env, pResult, method, self);

    if (isSynchronized) {
        dvmUnlockObject(self, lockObj);
    }
    if (method->shouldTrace) {
        logNativeMethodExit(method, self, *pResult);
    }
}

/*
 * Extract the return type enum from the "jniArgInfo" field.
 */
DalvikJniReturnType dvmGetArgInfoReturnType(int jniArgInfo) {
    return static_cast<DalvikJniReturnType>((jniArgInfo & DALVIK_JNI_RETURN_MASK) >> DALVIK_JNI_RETURN_SHIFT);
}

/*
 * ===========================================================================
 *      JNI implementation
 * ===========================================================================
 */

/*
 * Return the version of the native method interface.
 */
static jint GetVersion(JNIEnv* env) {
    /*
     * There is absolutely no need to toggle the mode for correct behavior.
     * However, it does provide native code with a simple "suspend self
     * if necessary" call.
     */
    ScopedJniThreadState ts(env);
    return JNI_VERSION_1_6;
}

/*
 * Create a new class from a bag of bytes.
 *
 * This is not currently supported within Dalvik.
 */
static jclass DefineClass(JNIEnv* env, const char *name, jobject loader,
    const jbyte* buf, jsize bufLen)
{
    UNUSED_PARAMETER(name);
    UNUSED_PARAMETER(loader);
    UNUSED_PARAMETER(buf);
    UNUSED_PARAMETER(bufLen);

    ScopedJniThreadState ts(env);
    LOGW("JNI DefineClass is not supported");
    return NULL;
}

/*
 * Find a class by name.
 *
 * We have to use the "no init" version of FindClass here, because we might
 * be getting the class prior to registering native methods that will be
 * used in <clinit>.
 *
 * We need to get the class loader associated with the current native
 * method.  If there is no native method, e.g. we're calling this from native
 * code right after creating the VM, the spec says we need to use the class
 * loader returned by "ClassLoader.getBaseClassLoader".  There is no such
 * method, but it's likely they meant ClassLoader.getSystemClassLoader.
 * We can't get that until after the VM has initialized though.
 */
static jclass FindClass(JNIEnv* env, const char* name) {
    ScopedJniThreadState ts(env);

    const Method* thisMethod = dvmGetCurrentJNIMethod();
    assert(thisMethod != NULL);

    Object* loader;
    Object* trackedLoader = NULL;
    if (ts.self()->classLoaderOverride != NULL) {
        /* hack for JNI_OnLoad */
        assert(strcmp(thisMethod->name, "nativeLoad") == 0);
        loader = ts.self()->classLoaderOverride;
    } else if (thisMethod == gDvm.methDalvikSystemNativeStart_main ||
               thisMethod == gDvm.methDalvikSystemNativeStart_run) {
        /* start point of invocation interface */
        if (!gDvm.initializing) {
            loader = trackedLoader = dvmGetSystemClassLoader();
        } else {
            loader = NULL;
        }
    } else {
        loader = thisMethod->clazz->classLoader;
    }

    char* descriptor = dvmNameToDescriptor(name);
    if (descriptor == NULL) {
        return NULL;
    }
    ClassObject* clazz = dvmFindClassNoInit(descriptor, loader);
    free(descriptor);

    jclass jclazz = (jclass) addLocalReference(env, (Object*) clazz);
    dvmReleaseTrackedAlloc(trackedLoader, ts.self());
    return jclazz;
}

/*
 * Return the superclass of a class.
 */
static jclass GetSuperclass(JNIEnv* env, jclass jclazz) {
    ScopedJniThreadState ts(env);
    ClassObject* clazz = (ClassObject*) dvmDecodeIndirectRef(env, jclazz);
    return (jclass) addLocalReference(env, (Object*)clazz->super);
}

/*
 * Determine whether an object of clazz1 can be safely cast to clazz2.
 *
 * Like IsInstanceOf, but with a pair of class objects instead of obj+class.
 */
static jboolean IsAssignableFrom(JNIEnv* env, jclass jclazz1, jclass jclazz2) {
    ScopedJniThreadState ts(env);
    ClassObject* clazz1 = (ClassObject*) dvmDecodeIndirectRef(env, jclazz1);
    ClassObject* clazz2 = (ClassObject*) dvmDecodeIndirectRef(env, jclazz2);
    return dvmInstanceof(clazz1, clazz2);
}

/*
 * Given a java.lang.reflect.Method or .Constructor, return a methodID.
 */
static jmethodID FromReflectedMethod(JNIEnv* env, jobject jmethod) {
    ScopedJniThreadState ts(env);
    Object* method = dvmDecodeIndirectRef(env, jmethod);
    return (jmethodID) dvmGetMethodFromReflectObj(method);
}

/*
 * Given a java.lang.reflect.Field, return a fieldID.
 */
static jfieldID FromReflectedField(JNIEnv* env, jobject jfield) {
    ScopedJniThreadState ts(env);
    Object* field = dvmDecodeIndirectRef(env, jfield);
    return (jfieldID) dvmGetFieldFromReflectObj(field);
}

/*
 * Convert a methodID to a java.lang.reflect.Method or .Constructor.
 *
 * (The "isStatic" field does not appear in the spec.)
 *
 * Throws OutOfMemory and returns NULL on failure.
 */
static jobject ToReflectedMethod(JNIEnv* env, jclass jcls, jmethodID methodID, jboolean isStatic) {
    ScopedJniThreadState ts(env);
    ClassObject* clazz = (ClassObject*) dvmDecodeIndirectRef(env, jcls);
    Object* obj = dvmCreateReflectObjForMethod(clazz, (Method*) methodID);
    dvmReleaseTrackedAlloc(obj, NULL);
    return addLocalReference(env, obj);
}

/*
 * Convert a fieldID to a java.lang.reflect.Field.
 *
 * (The "isStatic" field does not appear in the spec.)
 *
 * Throws OutOfMemory and returns NULL on failure.
 */
static jobject ToReflectedField(JNIEnv* env, jclass jcls, jfieldID fieldID, jboolean isStatic) {
    ScopedJniThreadState ts(env);
    ClassObject* clazz = (ClassObject*) dvmDecodeIndirectRef(env, jcls);
    Object* obj = dvmCreateReflectObjForField(clazz, (Field*) fieldID);
    dvmReleaseTrackedAlloc(obj, NULL);
    return addLocalReference(env, obj);
}

/*
 * Take this exception and throw it.
 */
static jint Throw(JNIEnv* env, jthrowable jobj) {
    ScopedJniThreadState ts(env);
    if (jobj != NULL) {
        Object* obj = dvmDecodeIndirectRef(env, jobj);
        dvmSetException(ts.self(), obj);
        return JNI_OK;
    }
    return JNI_ERR;
}

/*
 * Constructs an exception object from the specified class with the message
 * specified by "message", and throws it.
 */
static jint ThrowNew(JNIEnv* env, jclass jclazz, const char* message) {
    ScopedJniThreadState ts(env);
    ClassObject* clazz = (ClassObject*) dvmDecodeIndirectRef(env, jclazz);
    dvmThrowException(clazz, message);
    // TODO: should return failure if this didn't work (e.g. OOM)
    return JNI_OK;
}

/*
 * If an exception is being thrown, return the exception object.  Otherwise,
 * return NULL.
 *
 * TODO: if there is no pending exception, we should be able to skip the
 * enter/exit checks.  If we find one, we need to enter and then re-fetch
 * the exception (in case it got moved by a compacting GC).
 */
static jthrowable ExceptionOccurred(JNIEnv* env) {
    ScopedJniThreadState ts(env);
    Object* exception = dvmGetException(ts.self());
    jthrowable localException = (jthrowable) addLocalReference(env, exception);
    if (localException == NULL && exception != NULL) {
        /*
         * We were unable to add a new local reference, and threw a new
         * exception.  We can't return "exception", because it's not a
         * local reference.  So we have to return NULL, indicating that
         * there was no exception, even though it's pretty much raining
         * exceptions in here.
         */
        LOGW("JNI WARNING: addLocal/exception combo");
    }
    return localException;
}

/*
 * Print an exception and stack trace to stderr.
 */
static void ExceptionDescribe(JNIEnv* env) {
    ScopedJniThreadState ts(env);
    Object* exception = dvmGetException(ts.self());
    if (exception != NULL) {
        dvmPrintExceptionStackTrace();
    } else {
        LOGI("Odd: ExceptionDescribe called, but no exception pending");
    }
}

/*
 * Clear the exception currently being thrown.
 *
 * TODO: we should be able to skip the enter/exit stuff.
 */
static void ExceptionClear(JNIEnv* env) {
    ScopedJniThreadState ts(env);
    dvmClearException(ts.self());
}

/*
 * Kill the VM.  This function does not return.
 */
static void FatalError(JNIEnv* env, const char* msg) {
    //dvmChangeStatus(NULL, THREAD_RUNNING);
    LOGE("JNI posting fatal error: %s", msg);
    dvmAbort();
}

/*
 * Push a new JNI frame on the stack, with a new set of locals.
 *
 * The new frame must have the same method pointer.  (If for no other
 * reason than FindClass needs it to get the appropriate class loader.)
 */
static jint PushLocalFrame(JNIEnv* env, jint capacity) {
    ScopedJniThreadState ts(env);
    if (!ensureLocalCapacity(env, capacity) ||
            !dvmPushLocalFrame(ts.self(), dvmGetCurrentJNIMethod()))
    {
        /* yes, OutOfMemoryError, not StackOverflowError */
        dvmClearException(ts.self());
        dvmThrowOutOfMemoryError("out of stack in JNI PushLocalFrame");
        return JNI_ERR;
    }
    return JNI_OK;
}

/*
 * Pop the local frame off.  If "jresult" is not null, add it as a
 * local reference on the now-current frame.
 */
static jobject PopLocalFrame(JNIEnv* env, jobject jresult) {
    ScopedJniThreadState ts(env);
    Object* result = dvmDecodeIndirectRef(env, jresult);
    if (!dvmPopLocalFrame(ts.self())) {
        LOGW("JNI WARNING: too many PopLocalFrame calls");
        dvmClearException(ts.self());
        dvmThrowRuntimeException("too many PopLocalFrame calls");
    }
    return addLocalReference(env, result);
}

/*
 * Add a reference to the global list.
 */
static jobject NewGlobalRef(JNIEnv* env, jobject jobj) {
    ScopedJniThreadState ts(env);
    Object* obj = dvmDecodeIndirectRef(env, jobj);
    return addGlobalReference(obj);
}

/*
 * Delete a reference from the global list.
 */
static void DeleteGlobalRef(JNIEnv* env, jobject jglobalRef) {
    ScopedJniThreadState ts(env);
    deleteGlobalReference(jglobalRef);
}


/*
 * Add a reference to the local list.
 */
static jobject NewLocalRef(JNIEnv* env, jobject jobj) {
    ScopedJniThreadState ts(env);
    Object* obj = dvmDecodeIndirectRef(env, jobj);
    return addLocalReference(env, obj);
}

/*
 * Delete a reference from the local list.
 */
static void DeleteLocalRef(JNIEnv* env, jobject jlocalRef) {
    ScopedJniThreadState ts(env);
    deleteLocalReference(env, jlocalRef);
}

/*
 * Ensure that the local references table can hold at least this many
 * references.
 */
static jint EnsureLocalCapacity(JNIEnv* env, jint capacity) {
    ScopedJniThreadState ts(env);
    bool okay = ensureLocalCapacity(env, capacity);
    if (!okay) {
        dvmThrowOutOfMemoryError("can't ensure local reference capacity");
    }
    return okay ? 0 : -1;
}


/*
 * Determine whether two Object references refer to the same underlying object.
 */
static jboolean IsSameObject(JNIEnv* env, jobject jref1, jobject jref2) {
    ScopedJniThreadState ts(env);
    Object* obj1 = dvmDecodeIndirectRef(env, jref1);
    Object* obj2 = dvmDecodeIndirectRef(env, jref2);
    return (obj1 == obj2);
}

/*
 * Allocate a new object without invoking any constructors.
 */
static jobject AllocObject(JNIEnv* env, jclass jclazz) {
    ScopedJniThreadState ts(env);

    ClassObject* clazz = (ClassObject*) dvmDecodeIndirectRef(env, jclazz);
    if (!canAllocClass(clazz) ||
        (!dvmIsClassInitialized(clazz) && !dvmInitClass(clazz)))
    {
        assert(dvmCheckException(ts.self()));
        return NULL;
    }

    Object* newObj = dvmAllocObject(clazz, ALLOC_DONT_TRACK);
    return addLocalReference(env, newObj);
}

/*
 * Allocate a new object and invoke the supplied constructor.
 */
static jobject NewObject(JNIEnv* env, jclass jclazz, jmethodID methodID, ...) {
    ScopedJniThreadState ts(env);
    ClassObject* clazz = (ClassObject*) dvmDecodeIndirectRef(env, jclazz);

    if (!canAllocClass(clazz) || (!dvmIsClassInitialized(clazz) && !dvmInitClass(clazz))) {
        assert(dvmCheckException(ts.self()));
        return NULL;
    }

    Object* newObj = dvmAllocObject(clazz, ALLOC_DONT_TRACK);
    jobject result = addLocalReference(env, newObj);
    if (newObj != NULL) {
        JValue unused;
        va_list args;
        va_start(args, methodID);
        dvmCallMethodV(ts.self(), (Method*) methodID, newObj, true, &unused, args);
        va_end(args);
    }
    return result;
}

static jobject NewObjectV(JNIEnv* env, jclass jclazz, jmethodID methodID, va_list args) {
    ScopedJniThreadState ts(env);
    ClassObject* clazz = (ClassObject*) dvmDecodeIndirectRef(env, jclazz);

    if (!canAllocClass(clazz) || (!dvmIsClassInitialized(clazz) && !dvmInitClass(clazz))) {
        assert(dvmCheckException(ts.self()));
        return NULL;
    }

    Object* newObj = dvmAllocObject(clazz, ALLOC_DONT_TRACK);
    jobject result = addLocalReference(env, newObj);
    if (newObj != NULL) {
        JValue unused;
        dvmCallMethodV(ts.self(), (Method*) methodID, newObj, true, &unused, args);
    }
    return result;
}

static jobject NewObjectA(JNIEnv* env, jclass jclazz, jmethodID methodID, jvalue* args) {
    ScopedJniThreadState ts(env);
    ClassObject* clazz = (ClassObject*) dvmDecodeIndirectRef(env, jclazz);

    if (!canAllocClass(clazz) || (!dvmIsClassInitialized(clazz) && !dvmInitClass(clazz))) {
        assert(dvmCheckException(ts.self()));
        return NULL;
    }

    Object* newObj = dvmAllocObject(clazz, ALLOC_DONT_TRACK);
    jobject result = addLocalReference(env, newObj);
    if (newObj != NULL) {
        JValue unused;
        dvmCallMethodA(ts.self(), (Method*) methodID, newObj, true, &unused, args);
    }
    return result;
}

/*
 * Returns the class of an object.
 *
 * JNI spec says: obj must not be NULL.
 */
static jclass GetObjectClass(JNIEnv* env, jobject jobj) {
    ScopedJniThreadState ts(env);

    assert(jobj != NULL);

    Object* obj = dvmDecodeIndirectRef(env, jobj);
    return (jclass) addLocalReference(env, (Object*) obj->clazz);
}

/*
 * Determine whether "obj" is an instance of "clazz".
 */
static jboolean IsInstanceOf(JNIEnv* env, jobject jobj, jclass jclazz) {
    ScopedJniThreadState ts(env);

    assert(jclazz != NULL);
    if (jobj == NULL) {
        return true;
    }

    Object* obj = dvmDecodeIndirectRef(env, jobj);
    ClassObject* clazz = (ClassObject*) dvmDecodeIndirectRef(env, jclazz);
    return dvmInstanceof(obj->clazz, clazz);
}

/*
 * Get a method ID for an instance method.
 *
 * While Dalvik bytecode has distinct instructions for virtual, super,
 * static, direct, and interface method invocation, JNI only provides
 * two functions for acquiring a method ID.  This call handles everything
 * but static methods.
 *
 * JNI defines <init> as an instance method, but Dalvik considers it a
 * "direct" method, so we have to special-case it here.
 *
 * Dalvik also puts all private methods into the "direct" list, so we
 * really need to just search both lists.
 */
static jmethodID GetMethodID(JNIEnv* env, jclass jclazz, const char* name, const char* sig) {
    ScopedJniThreadState ts(env);

    ClassObject* clazz = (ClassObject*) dvmDecodeIndirectRef(env, jclazz);
    if (!dvmIsClassInitialized(clazz) && !dvmInitClass(clazz)) {
        assert(dvmCheckException(ts.self()));
    } else if (dvmIsInterfaceClass(clazz)) {
        Method* meth = dvmFindInterfaceMethodHierByDescriptor(clazz, name, sig);
        if (meth == NULL) {
            dvmThrowExceptionFmt(gDvm.exNoSuchMethodError,
                "no method with name='%s' signature='%s' in interface %s",
                name, sig, clazz->descriptor);
        }
        return (jmethodID) meth;
    }
    Method* meth = dvmFindVirtualMethodHierByDescriptor(clazz, name, sig);
    if (meth == NULL) {
        /* search private methods and constructors; non-hierarchical */
        meth = dvmFindDirectMethodByDescriptor(clazz, name, sig);
    }
    if (meth != NULL && dvmIsStaticMethod(meth)) {
        IF_LOGD() {
            char* desc = dexProtoCopyMethodDescriptor(&meth->prototype);
            LOGD("GetMethodID: not returning static method %s.%s %s",
                    clazz->descriptor, meth->name, desc);
            free(desc);
        }
        meth = NULL;
    }
    if (meth == NULL) {
        dvmThrowExceptionFmt(gDvm.exNoSuchMethodError,
                "no method with name='%s' signature='%s' in class %s",
                name, sig, clazz->descriptor);
    } else {
        /*
         * The method's class may not be the same as clazz, but if
         * it isn't this must be a virtual method and the class must
         * be a superclass (and, hence, already initialized).
         */
        assert(dvmIsClassInitialized(meth->clazz) || dvmIsClassInitializing(meth->clazz));
    }
    return (jmethodID) meth;
}

/*
 * Get a field ID (instance fields).
 */
static jfieldID GetFieldID(JNIEnv* env, jclass jclazz, const char* name, const char* sig) {
    ScopedJniThreadState ts(env);

    ClassObject* clazz = (ClassObject*) dvmDecodeIndirectRef(env, jclazz);

    if (!dvmIsClassInitialized(clazz) && !dvmInitClass(clazz)) {
        assert(dvmCheckException(ts.self()));
        return NULL;
    }

    jfieldID id = (jfieldID) dvmFindInstanceFieldHier(clazz, name, sig);
    if (id == NULL) {
        dvmThrowExceptionFmt(gDvm.exNoSuchFieldError,
                "no field with name='%s' signature='%s' in class %s",
                name, sig, clazz->descriptor);
    }
    return id;
}

/*
 * Get the method ID for a static method in a class.
 */
static jmethodID GetStaticMethodID(JNIEnv* env, jclass jclazz, const char* name, const char* sig) {
    ScopedJniThreadState ts(env);

    ClassObject* clazz = (ClassObject*) dvmDecodeIndirectRef(env, jclazz);
    if (!dvmIsClassInitialized(clazz) && !dvmInitClass(clazz)) {
        assert(dvmCheckException(ts.self()));
        return NULL;
    }

    Method* meth = dvmFindDirectMethodHierByDescriptor(clazz, name, sig);

    /* make sure it's static, not virtual+private */
    if (meth != NULL && !dvmIsStaticMethod(meth)) {
        IF_LOGD() {
            char* desc = dexProtoCopyMethodDescriptor(&meth->prototype);
            LOGD("GetStaticMethodID: not returning nonstatic method %s.%s %s",
                    clazz->descriptor, meth->name, desc);
            free(desc);
        }
        meth = NULL;
    }

    jmethodID id = (jmethodID) meth;
    if (id == NULL) {
        dvmThrowExceptionFmt(gDvm.exNoSuchMethodError,
                "no static method with name='%s' signature='%s' in class %s",
                name, sig, clazz->descriptor);
    }
    return id;
}

/*
 * Get a field ID (static fields).
 */
static jfieldID GetStaticFieldID(JNIEnv* env, jclass jclazz, const char* name, const char* sig) {
    ScopedJniThreadState ts(env);

    ClassObject* clazz = (ClassObject*) dvmDecodeIndirectRef(env, jclazz);
    if (!dvmIsClassInitialized(clazz) && !dvmInitClass(clazz)) {
        assert(dvmCheckException(ts.self()));
        return NULL;
    }

    jfieldID id = (jfieldID) dvmFindStaticFieldHier(clazz, name, sig);
    if (id == NULL) {
        dvmThrowExceptionFmt(gDvm.exNoSuchFieldError,
                "no static field with name='%s' signature='%s' in class %s",
                name, sig, clazz->descriptor);
    }
    return id;
}

/*
 * Get a static field.
 *
 * If we get an object reference, add it to the local refs list.
 */
#define GET_STATIC_TYPE_FIELD(_ctype, _jname, _isref)                       \
    static _ctype GetStatic##_jname##Field(JNIEnv* env, jclass jclazz,      \
        jfieldID fieldID)                                                   \
    {                                                                       \
        UNUSED_PARAMETER(jclazz);                                           \
        ScopedJniThreadState ts(env);                                       \
        StaticField* sfield = (StaticField*) fieldID;                       \
        _ctype value;                                                       \
        if (dvmIsVolatileField(sfield)) {                                   \
            if (_isref) {   /* only when _ctype==jobject */                 \
                Object* obj = dvmGetStaticFieldObjectVolatile(sfield);      \
                value = (_ctype)(u4)addLocalReference(env, obj);            \
            } else {                                                        \
                value = (_ctype) dvmGetStaticField##_jname##Volatile(sfield);\
            }                                                               \
        } else {                                                            \
            if (_isref) {                                                   \
                Object* obj = dvmGetStaticFieldObject(sfield);              \
                value = (_ctype)(u4)addLocalReference(env, obj);            \
            } else {                                                        \
                value = (_ctype) dvmGetStaticField##_jname(sfield);         \
            }                                                               \
        }                                                                   \
        return value;                                                       \
    }
GET_STATIC_TYPE_FIELD(jobject, Object, true);
GET_STATIC_TYPE_FIELD(jboolean, Boolean, false);
GET_STATIC_TYPE_FIELD(jbyte, Byte, false);
GET_STATIC_TYPE_FIELD(jchar, Char, false);
GET_STATIC_TYPE_FIELD(jshort, Short, false);
GET_STATIC_TYPE_FIELD(jint, Int, false);
GET_STATIC_TYPE_FIELD(jlong, Long, false);
GET_STATIC_TYPE_FIELD(jfloat, Float, false);
GET_STATIC_TYPE_FIELD(jdouble, Double, false);

/*
 * Set a static field.
 */
#define SET_STATIC_TYPE_FIELD(_ctype, _ctype2, _jname, _isref)              \
    static void SetStatic##_jname##Field(JNIEnv* env, jclass jclazz,        \
        jfieldID fieldID, _ctype value)                                     \
    {                                                                       \
        UNUSED_PARAMETER(jclazz);                                           \
        ScopedJniThreadState ts(env);                                       \
        StaticField* sfield = (StaticField*) fieldID;                       \
        if (dvmIsVolatileField(sfield)) {                                   \
            if (_isref) {   /* only when _ctype==jobject */                 \
                Object* valObj =                                            \
                    dvmDecodeIndirectRef(env, (jobject)(u4)value);          \
                dvmSetStaticFieldObjectVolatile(sfield, valObj);            \
            } else {                                                        \
                dvmSetStaticField##_jname##Volatile(sfield, (_ctype2)value);\
            }                                                               \
        } else {                                                            \
            if (_isref) {                                                   \
                Object* valObj =                                            \
                    dvmDecodeIndirectRef(env, (jobject)(u4)value);          \
                dvmSetStaticFieldObject(sfield, valObj);                    \
            } else {                                                        \
                dvmSetStaticField##_jname(sfield, (_ctype2)value);          \
            }                                                               \
        }                                                                   \
    }
SET_STATIC_TYPE_FIELD(jobject, Object*, Object, true);
SET_STATIC_TYPE_FIELD(jboolean, bool, Boolean, false);
SET_STATIC_TYPE_FIELD(jbyte, s1, Byte, false);
SET_STATIC_TYPE_FIELD(jchar, u2, Char, false);
SET_STATIC_TYPE_FIELD(jshort, s2, Short, false);
SET_STATIC_TYPE_FIELD(jint, s4, Int, false);
SET_STATIC_TYPE_FIELD(jlong, s8, Long, false);
SET_STATIC_TYPE_FIELD(jfloat, float, Float, false);
SET_STATIC_TYPE_FIELD(jdouble, double, Double, false);

/*
 * Get an instance field.
 *
 * If we get an object reference, add it to the local refs list.
 */
#define GET_TYPE_FIELD(_ctype, _jname, _isref)                              \
    static _ctype Get##_jname##Field(JNIEnv* env, jobject jobj,             \
        jfieldID fieldID)                                                   \
    {                                                                       \
        ScopedJniThreadState ts(env);                                       \
        Object* obj = dvmDecodeIndirectRef(env, jobj);                      \
        InstField* field = (InstField*) fieldID;                            \
        _ctype value;                                                       \
        if (dvmIsVolatileField(field)) {                            \
            if (_isref) {   /* only when _ctype==jobject */                 \
                Object* valObj =                                            \
                    dvmGetFieldObjectVolatile(obj, field->byteOffset);      \
                value = (_ctype)(u4)addLocalReference(env, valObj);         \
            } else {                                                        \
                value = (_ctype)                                            \
                    dvmGetField##_jname##Volatile(obj, field->byteOffset);  \
            }                                                               \
        } else {                                                            \
            if (_isref) {                                                   \
                Object* valObj = dvmGetFieldObject(obj, field->byteOffset); \
                value = (_ctype)(u4)addLocalReference(env, valObj);         \
            } else {                                                        \
                value = (_ctype) dvmGetField##_jname(obj, field->byteOffset);\
            }                                                               \
        }                                                                   \
        return value;                                                       \
    }
GET_TYPE_FIELD(jobject, Object, true);
GET_TYPE_FIELD(jboolean, Boolean, false);
GET_TYPE_FIELD(jbyte, Byte, false);
GET_TYPE_FIELD(jchar, Char, false);
GET_TYPE_FIELD(jshort, Short, false);
GET_TYPE_FIELD(jint, Int, false);
GET_TYPE_FIELD(jlong, Long, false);
GET_TYPE_FIELD(jfloat, Float, false);
GET_TYPE_FIELD(jdouble, Double, false);

/*
 * Set an instance field.
 */
#define SET_TYPE_FIELD(_ctype, _ctype2, _jname, _isref)                     \
    static void Set##_jname##Field(JNIEnv* env, jobject jobj,               \
        jfieldID fieldID, _ctype value)                                     \
    {                                                                       \
        ScopedJniThreadState ts(env);                                       \
        Object* obj = dvmDecodeIndirectRef(env, jobj);                      \
        InstField* field = (InstField*) fieldID;                            \
        if (dvmIsVolatileField(field)) {                                    \
            if (_isref) {   /* only when _ctype==jobject */                 \
                Object* valObj =                                            \
                    dvmDecodeIndirectRef(env, (jobject)(u4)value);          \
                dvmSetFieldObjectVolatile(obj, field->byteOffset, valObj);  \
            } else {                                                        \
                dvmSetField##_jname##Volatile(obj,                          \
                    field->byteOffset, (_ctype2)value);                     \
            }                                                               \
        } else {                                                            \
            if (_isref) {                                                   \
                Object* valObj =                                            \
                    dvmDecodeIndirectRef(env, (jobject)(u4)value);          \
                dvmSetFieldObject(obj, field->byteOffset, valObj);          \
            } else {                                                        \
                dvmSetField##_jname(obj,                                    \
                    field->byteOffset, (_ctype2)value);                     \
            }                                                               \
        }                                                                   \
    }
SET_TYPE_FIELD(jobject, Object*, Object, true);
SET_TYPE_FIELD(jboolean, bool, Boolean, false);
SET_TYPE_FIELD(jbyte, s1, Byte, false);
SET_TYPE_FIELD(jchar, u2, Char, false);
SET_TYPE_FIELD(jshort, s2, Short, false);
SET_TYPE_FIELD(jint, s4, Int, false);
SET_TYPE_FIELD(jlong, s8, Long, false);
SET_TYPE_FIELD(jfloat, float, Float, false);
SET_TYPE_FIELD(jdouble, double, Double, false);

/*
 * Make a virtual method call.
 *
 * Three versions (..., va_list, jvalue[]) for each return type.  If we're
 * returning an Object, we have to add it to the local references table.
 */
#define CALL_VIRTUAL(_ctype, _jname, _retfail, _retok, _isref)              \
    static _ctype Call##_jname##Method(JNIEnv* env, jobject jobj,           \
        jmethodID methodID, ...)                                            \
    {                                                                       \
        ScopedJniThreadState ts(env);                                       \
        Object* obj = dvmDecodeIndirectRef(env, jobj);                      \
        const Method* meth;                                                 \
        va_list args;                                                       \
        JValue result;                                                      \
        meth = dvmGetVirtualizedMethod(obj->clazz, (Method*)methodID);      \
        if (meth == NULL) {                                                 \
            return _retfail;                                                \
        }                                                                   \
        va_start(args, methodID);                                           \
        dvmCallMethodV(ts.self(), meth, obj, true, &result, args);          \
        va_end(args);                                                       \
        if (_isref && !dvmCheckException(ts.self()))                        \
            result.l = (Object*)addLocalReference(env, result.l);           \
        return _retok;                                                      \
    }                                                                       \
    static _ctype Call##_jname##MethodV(JNIEnv* env, jobject jobj,          \
        jmethodID methodID, va_list args)                                   \
    {                                                                       \
        ScopedJniThreadState ts(env);                                       \
        Object* obj = dvmDecodeIndirectRef(env, jobj);                      \
        const Method* meth;                                                 \
        JValue result;                                                      \
        meth = dvmGetVirtualizedMethod(obj->clazz, (Method*)methodID);      \
        if (meth == NULL) {                                                 \
            return _retfail;                                                \
        }                                                                   \
        dvmCallMethodV(ts.self(), meth, obj, true, &result, args);          \
        if (_isref && !dvmCheckException(ts.self()))                        \
            result.l = (Object*)addLocalReference(env, result.l);           \
        return _retok;                                                      \
    }                                                                       \
    static _ctype Call##_jname##MethodA(JNIEnv* env, jobject jobj,          \
        jmethodID methodID, jvalue* args)                                   \
    {                                                                       \
        ScopedJniThreadState ts(env);                                       \
        Object* obj = dvmDecodeIndirectRef(env, jobj);                      \
        const Method* meth;                                                 \
        JValue result;                                                      \
        meth = dvmGetVirtualizedMethod(obj->clazz, (Method*)methodID);      \
        if (meth == NULL) {                                                 \
            return _retfail;                                                \
        }                                                                   \
        dvmCallMethodA(ts.self(), meth, obj, true, &result, args);          \
        if (_isref && !dvmCheckException(ts.self()))                        \
            result.l = (Object*)addLocalReference(env, result.l);           \
        return _retok;                                                      \
    }
CALL_VIRTUAL(jobject, Object, NULL, (jobject) result.l, true);
CALL_VIRTUAL(jboolean, Boolean, 0, result.z, false);
CALL_VIRTUAL(jbyte, Byte, 0, result.b, false);
CALL_VIRTUAL(jchar, Char, 0, result.c, false);
CALL_VIRTUAL(jshort, Short, 0, result.s, false);
CALL_VIRTUAL(jint, Int, 0, result.i, false);
CALL_VIRTUAL(jlong, Long, 0, result.j, false);
CALL_VIRTUAL(jfloat, Float, 0.0f, result.f, false);
CALL_VIRTUAL(jdouble, Double, 0.0, result.d, false);
CALL_VIRTUAL(void, Void, , , false);

/*
 * Make a "non-virtual" method call.  We're still calling a virtual method,
 * but this time we're not doing an indirection through the object's vtable.
 * The "clazz" parameter defines which implementation of a method we want.
 *
 * Three versions (..., va_list, jvalue[]) for each return type.
 */
#define CALL_NONVIRTUAL(_ctype, _jname, _retfail, _retok, _isref)           \
    static _ctype CallNonvirtual##_jname##Method(JNIEnv* env, jobject jobj, \
        jclass jclazz, jmethodID methodID, ...)                             \
    {                                                                       \
        ScopedJniThreadState ts(env);                                       \
        Object* obj = dvmDecodeIndirectRef(env, jobj);                      \
        ClassObject* clazz =                                                \
            (ClassObject*) dvmDecodeIndirectRef(env, jclazz);               \
        const Method* meth;                                                 \
        va_list args;                                                       \
        JValue result;                                                      \
        meth = dvmGetVirtualizedMethod(clazz, (Method*)methodID);           \
        if (meth == NULL) {                                                 \
            return _retfail;                                                \
        }                                                                   \
        va_start(args, methodID);                                           \
        dvmCallMethodV(ts.self(), meth, obj, true, &result, args);          \
        if (_isref && !dvmCheckException(ts.self()))                        \
            result.l = (Object*)addLocalReference(env, result.l);           \
        va_end(args);                                                       \
        return _retok;                                                      \
    }                                                                       \
    static _ctype CallNonvirtual##_jname##MethodV(JNIEnv* env, jobject jobj,\
        jclass jclazz, jmethodID methodID, va_list args)                    \
    {                                                                       \
        ScopedJniThreadState ts(env);                                       \
        Object* obj = dvmDecodeIndirectRef(env, jobj);                      \
        ClassObject* clazz =                                                \
            (ClassObject*) dvmDecodeIndirectRef(env, jclazz);               \
        const Method* meth;                                                 \
        JValue result;                                                      \
        meth = dvmGetVirtualizedMethod(clazz, (Method*)methodID);           \
        if (meth == NULL) {                                                 \
            return _retfail;                                                \
        }                                                                   \
        dvmCallMethodV(ts.self(), meth, obj, true, &result, args);          \
        if (_isref && !dvmCheckException(ts.self()))                        \
            result.l = (Object*)addLocalReference(env, result.l);           \
        return _retok;                                                      \
    }                                                                       \
    static _ctype CallNonvirtual##_jname##MethodA(JNIEnv* env, jobject jobj,\
        jclass jclazz, jmethodID methodID, jvalue* args)                    \
    {                                                                       \
        ScopedJniThreadState ts(env);                                       \
        Object* obj = dvmDecodeIndirectRef(env, jobj);                      \
        ClassObject* clazz =                                                \
            (ClassObject*) dvmDecodeIndirectRef(env, jclazz);               \
        const Method* meth;                                                 \
        JValue result;                                                      \
        meth = dvmGetVirtualizedMethod(clazz, (Method*)methodID);           \
        if (meth == NULL) {                                                 \
            return _retfail;                                                \
        }                                                                   \
        dvmCallMethodA(ts.self(), meth, obj, true, &result, args);          \
        if (_isref && !dvmCheckException(ts.self()))                        \
            result.l = (Object*)addLocalReference(env, result.l);           \
        return _retok;                                                      \
    }
CALL_NONVIRTUAL(jobject, Object, NULL, (jobject) result.l, true);
CALL_NONVIRTUAL(jboolean, Boolean, 0, result.z, false);
CALL_NONVIRTUAL(jbyte, Byte, 0, result.b, false);
CALL_NONVIRTUAL(jchar, Char, 0, result.c, false);
CALL_NONVIRTUAL(jshort, Short, 0, result.s, false);
CALL_NONVIRTUAL(jint, Int, 0, result.i, false);
CALL_NONVIRTUAL(jlong, Long, 0, result.j, false);
CALL_NONVIRTUAL(jfloat, Float, 0.0f, result.f, false);
CALL_NONVIRTUAL(jdouble, Double, 0.0, result.d, false);
CALL_NONVIRTUAL(void, Void, , , false);


/*
 * Call a static method.
 */
#define CALL_STATIC(_ctype, _jname, _retfail, _retok, _isref)               \
    static _ctype CallStatic##_jname##Method(JNIEnv* env, jclass jclazz,    \
        jmethodID methodID, ...)                                            \
    {                                                                       \
        UNUSED_PARAMETER(jclazz);                                           \
        ScopedJniThreadState ts(env);                                       \
        JValue result;                                                      \
        va_list args;                                                       \
        va_start(args, methodID);                                           \
        dvmCallMethodV(ts.self(), (Method*)methodID, NULL, true, &result, args);\
        va_end(args);                                                       \
        if (_isref && !dvmCheckException(ts.self()))                        \
            result.l = (Object*)addLocalReference(env, result.l);           \
        return _retok;                                                      \
    }                                                                       \
    static _ctype CallStatic##_jname##MethodV(JNIEnv* env, jclass jclazz,   \
        jmethodID methodID, va_list args)                                   \
    {                                                                       \
        UNUSED_PARAMETER(jclazz);                                           \
        ScopedJniThreadState ts(env);                                       \
        JValue result;                                                      \
        dvmCallMethodV(ts.self(), (Method*)methodID, NULL, true, &result, args);\
        if (_isref && !dvmCheckException(ts.self()))                        \
            result.l = (Object*)addLocalReference(env, result.l);           \
        return _retok;                                                      \
    }                                                                       \
    static _ctype CallStatic##_jname##MethodA(JNIEnv* env, jclass jclazz,   \
        jmethodID methodID, jvalue* args)                                   \
    {                                                                       \
        UNUSED_PARAMETER(jclazz);                                           \
        ScopedJniThreadState ts(env);                                       \
        JValue result;                                                      \
        dvmCallMethodA(ts.self(), (Method*)methodID, NULL, true, &result, args);\
        if (_isref && !dvmCheckException(ts.self()))                        \
            result.l = (Object*)addLocalReference(env, result.l);           \
        return _retok;                                                      \
    }
CALL_STATIC(jobject, Object, NULL, (jobject) result.l, true);
CALL_STATIC(jboolean, Boolean, 0, result.z, false);
CALL_STATIC(jbyte, Byte, 0, result.b, false);
CALL_STATIC(jchar, Char, 0, result.c, false);
CALL_STATIC(jshort, Short, 0, result.s, false);
CALL_STATIC(jint, Int, 0, result.i, false);
CALL_STATIC(jlong, Long, 0, result.j, false);
CALL_STATIC(jfloat, Float, 0.0f, result.f, false);
CALL_STATIC(jdouble, Double, 0.0, result.d, false);
CALL_STATIC(void, Void, , , false);

/*
 * Create a new String from Unicode data.
 *
 * If "len" is zero, we will return an empty string even if "unicodeChars"
 * is NULL.  (The JNI spec is vague here.)
 */
static jstring NewString(JNIEnv* env, const jchar* unicodeChars, jsize len) {
    ScopedJniThreadState ts(env);
    StringObject* jstr = dvmCreateStringFromUnicode(unicodeChars, len);
    if (jstr == NULL) {
        return NULL;
    }
    dvmReleaseTrackedAlloc((Object*) jstr, NULL);
    return (jstring) addLocalReference(env, (Object*) jstr);
}

/*
 * Return the length of a String in Unicode character units.
 */
static jsize GetStringLength(JNIEnv* env, jstring jstr) {
    ScopedJniThreadState ts(env);
    StringObject* strObj = (StringObject*) dvmDecodeIndirectRef(env, jstr);
    return strObj->length();
}


/*
 * Get a string's character data.
 *
 * The result is guaranteed to be valid until ReleaseStringChars is
 * called, which means we have to pin it or return a copy.
 */
static const jchar* GetStringChars(JNIEnv* env, jstring jstr, jboolean* isCopy) {
    ScopedJniThreadState ts(env);

    StringObject* strObj = (StringObject*) dvmDecodeIndirectRef(env, jstr);
    ArrayObject* strChars = strObj->array();

    pinPrimitiveArray(strChars);

    const u2* data = strObj->chars();
    if (isCopy != NULL) {
        *isCopy = JNI_FALSE;
    }
    return (jchar*) data;
}

/*
 * Release our grip on some characters from a string.
 */
static void ReleaseStringChars(JNIEnv* env, jstring jstr, const jchar* chars) {
    ScopedJniThreadState ts(env);
    StringObject* strObj = (StringObject*) dvmDecodeIndirectRef(env, jstr);
    ArrayObject* strChars = strObj->array();
    unpinPrimitiveArray(strChars);
}

/*
 * Create a new java.lang.String object from chars in modified UTF-8 form.
 *
 * The spec doesn't say how to handle a NULL string.  Popular desktop VMs
 * accept it and return a NULL pointer in response.
 */
static jstring NewStringUTF(JNIEnv* env, const char* bytes) {
    ScopedJniThreadState ts(env);
    if (bytes == NULL) {
        return NULL;
    }
    /* note newStr could come back NULL on OOM */
    StringObject* newStr = dvmCreateStringFromCstr(bytes);
    jstring result = (jstring) addLocalReference(env, (Object*) newStr);
    dvmReleaseTrackedAlloc((Object*)newStr, NULL);
    return result;
}

/*
 * Return the length in bytes of the modified UTF-8 form of the string.
 */
static jsize GetStringUTFLength(JNIEnv* env, jstring jstr) {
    ScopedJniThreadState ts(env);
    StringObject* strObj = (StringObject*) dvmDecodeIndirectRef(env, jstr);
    if (strObj == NULL) {
        return 0; // Should we throw something or assert?
    }
    return strObj->utfLength();
}

/*
 * Convert "string" to modified UTF-8 and return a pointer.  The returned
 * value must be released with ReleaseStringUTFChars.
 *
 * According to the JNI reference, "Returns a pointer to a UTF-8 string,
 * or NULL if the operation fails. Returns NULL if and only if an invocation
 * of this function has thrown an exception."
 *
 * The behavior here currently follows that of other open-source VMs, which
 * quietly return NULL if "string" is NULL.  We should consider throwing an
 * NPE.  (The CheckJNI code blows up if you try to pass in a NULL string,
 * which should catch this sort of thing during development.)  Certain other
 * VMs will crash with a segmentation fault.
 */
static const char* GetStringUTFChars(JNIEnv* env, jstring jstr, jboolean* isCopy) {
    ScopedJniThreadState ts(env);
    if (jstr == NULL) {
        /* this shouldn't happen; throw NPE? */
        return NULL;
    }
    if (isCopy != NULL) {
        *isCopy = JNI_TRUE;
    }
    StringObject* strObj = (StringObject*) dvmDecodeIndirectRef(env, jstr);
    char* newStr = dvmCreateCstrFromString(strObj);
    if (newStr == NULL) {
        /* assume memory failure */
        dvmThrowOutOfMemoryError("native heap string alloc failed");
    }
    return newStr;
}

/*
 * Release a string created by GetStringUTFChars().
 */
static void ReleaseStringUTFChars(JNIEnv* env, jstring jstr, const char* utf) {
    ScopedJniThreadState ts(env);
    free((char*) utf);
}

/*
 * Return the capacity of the array.
 */
static jsize GetArrayLength(JNIEnv* env, jarray jarr) {
    ScopedJniThreadState ts(env);
    ArrayObject* arrObj = (ArrayObject*) dvmDecodeIndirectRef(env, jarr);
    return arrObj->length;
}

/*
 * Construct a new array that holds objects from class "elementClass".
 */
static jobjectArray NewObjectArray(JNIEnv* env, jsize length,
    jclass jelementClass, jobject jinitialElement)
{
    ScopedJniThreadState ts(env);

    if (jelementClass == NULL) {
        dvmThrowNullPointerException("JNI NewObjectArray elementClass == NULL");
        return NULL;
    }

    ClassObject* elemClassObj = (ClassObject*) dvmDecodeIndirectRef(env, jelementClass);
    ClassObject* arrayClass = dvmFindArrayClassForElement(elemClassObj);
    ArrayObject* newObj = dvmAllocArrayByClass(arrayClass, length, ALLOC_DEFAULT);
    if (newObj == NULL) {
        assert(dvmCheckException(ts.self()));
        return NULL;
    }
    jobjectArray newArray = (jobjectArray) addLocalReference(env, (Object*) newObj);
    dvmReleaseTrackedAlloc((Object*) newObj, NULL);

    /*
     * Initialize the array.
     */
    if (jinitialElement != NULL) {
        Object* initialElement = dvmDecodeIndirectRef(env, jinitialElement);
        Object** arrayData = (Object**) (void*) newObj->contents;
        for (jsize i = 0; i < length; ++i) {
            arrayData[i] = initialElement;
        }
    }

    return newArray;
}

static bool checkArrayElementBounds(ArrayObject* arrayObj, jsize index) {
    assert(arrayObj != NULL);
    if (index < 0 || index >= (int) arrayObj->length) {
        dvmThrowArrayIndexOutOfBoundsException(arrayObj->length, index);
        return false;
    }
    return true;
}

/*
 * Get one element of an Object array.
 *
 * Add the object to the local references table in case the array goes away.
 */
static jobject GetObjectArrayElement(JNIEnv* env, jobjectArray jarr, jsize index) {
    ScopedJniThreadState ts(env);

    ArrayObject* arrayObj = (ArrayObject*) dvmDecodeIndirectRef(env, jarr);
    if (!checkArrayElementBounds(arrayObj, index)) {
        return NULL;
    }

    Object* value = ((Object**) (void*) arrayObj->contents)[index];
    return addLocalReference(env, value);
}

/*
 * Set one element of an Object array.
 */
static void SetObjectArrayElement(JNIEnv* env, jobjectArray jarr, jsize index, jobject jobj) {
    ScopedJniThreadState ts(env);

    ArrayObject* arrayObj = (ArrayObject*) dvmDecodeIndirectRef(env, jarr);
    if (!checkArrayElementBounds(arrayObj, index)) {
        return;
    }

    //LOGV("JNI: set element %d in array %p to %p", index, array, value);

    Object* obj = dvmDecodeIndirectRef(env, jobj);
    dvmSetObjectArrayElement(arrayObj, index, obj);
}

/*
 * Create a new array of primitive elements.
 */
#define NEW_PRIMITIVE_ARRAY(_artype, _jname, _typechar) \
    static _artype New##_jname##Array(JNIEnv* env, jsize length) { \
        ScopedJniThreadState ts(env); \
        ArrayObject* arrayObj = dvmAllocPrimitiveArray(_typechar, length, ALLOC_DEFAULT); \
        if (arrayObj == NULL) { \
            return NULL; \
        } \
        _artype result = (_artype) addLocalReference(env, (Object*) arrayObj); \
        dvmReleaseTrackedAlloc((Object*) arrayObj, NULL); \
        return result; \
    }
NEW_PRIMITIVE_ARRAY(jbooleanArray, Boolean, 'Z');
NEW_PRIMITIVE_ARRAY(jbyteArray, Byte, 'B');
NEW_PRIMITIVE_ARRAY(jcharArray, Char, 'C');
NEW_PRIMITIVE_ARRAY(jshortArray, Short, 'S');
NEW_PRIMITIVE_ARRAY(jintArray, Int, 'I');
NEW_PRIMITIVE_ARRAY(jlongArray, Long, 'J');
NEW_PRIMITIVE_ARRAY(jfloatArray, Float, 'F');
NEW_PRIMITIVE_ARRAY(jdoubleArray, Double, 'D');

/*
 * Get a pointer to a C array of primitive elements from an array object
 * of the matching type.
 *
 * In a compacting GC, we either need to return a copy of the elements or
 * "pin" the memory.  Otherwise we run the risk of native code using the
 * buffer as the destination of e.g. a blocking read() call that wakes up
 * during a GC.
 */
#define GET_PRIMITIVE_ARRAY_ELEMENTS(_ctype, _jname) \
    static _ctype* Get##_jname##ArrayElements(JNIEnv* env, \
        _ctype##Array jarr, jboolean* isCopy) \
    { \
        ScopedJniThreadState ts(env); \
        ArrayObject* arrayObj = (ArrayObject*) dvmDecodeIndirectRef(env, jarr); \
        pinPrimitiveArray(arrayObj); \
        _ctype* data = (_ctype*) (void*) arrayObj->contents; \
        if (isCopy != NULL) { \
            *isCopy = JNI_FALSE; \
        } \
        return data; \
    }

/*
 * Release the storage locked down by the "get" function.
 *
 * The spec says, "'mode' has no effect if 'elems' is not a copy of the
 * elements in 'array'."  They apparently did not anticipate the need to
 * un-pin memory.
 */
#define RELEASE_PRIMITIVE_ARRAY_ELEMENTS(_ctype, _jname)                    \
    static void Release##_jname##ArrayElements(JNIEnv* env,                 \
        _ctype##Array jarr, _ctype* elems, jint mode)                       \
    {                                                                       \
        UNUSED_PARAMETER(elems);                                            \
        if (mode != JNI_COMMIT) {                                           \
            ScopedJniThreadState ts(env);                                   \
            ArrayObject* arrayObj =                                         \
                (ArrayObject*) dvmDecodeIndirectRef(env, jarr);             \
            unpinPrimitiveArray(arrayObj);                                  \
        }                                                                   \
    }

static void throwArrayRegionOutOfBounds(ArrayObject* arrayObj, jsize start,
    jsize len, const char* arrayIdentifier)
{
    dvmThrowExceptionFmt(gDvm.exArrayIndexOutOfBoundsException,
        "%s offset=%d length=%d %s.length=%d",
        arrayObj->clazz->descriptor, start, len, arrayIdentifier,
        arrayObj->length);
}

/*
 * Copy a section of a primitive array to a buffer.
 */
#define GET_PRIMITIVE_ARRAY_REGION(_ctype, _jname) \
    static void Get##_jname##ArrayRegion(JNIEnv* env, \
        _ctype##Array jarr, jsize start, jsize len, _ctype* buf) \
    { \
        ScopedJniThreadState ts(env); \
        ArrayObject* arrayObj = (ArrayObject*) dvmDecodeIndirectRef(env, jarr); \
        _ctype* data = (_ctype*) (void*) arrayObj->contents; \
        if (start < 0 || len < 0 || start + len > (int) arrayObj->length) { \
            throwArrayRegionOutOfBounds(arrayObj, start, len, "src"); \
        } else { \
            memcpy(buf, data + start, len * sizeof(_ctype)); \
        } \
    }

/*
 * Copy a section of a primitive array from a buffer.
 */
#define SET_PRIMITIVE_ARRAY_REGION(_ctype, _jname) \
    static void Set##_jname##ArrayRegion(JNIEnv* env, \
        _ctype##Array jarr, jsize start, jsize len, const _ctype* buf) \
    { \
        ScopedJniThreadState ts(env); \
        ArrayObject* arrayObj = (ArrayObject*) dvmDecodeIndirectRef(env, jarr); \
        _ctype* data = (_ctype*) (void*) arrayObj->contents; \
        if (start < 0 || len < 0 || start + len > (int) arrayObj->length) { \
            throwArrayRegionOutOfBounds(arrayObj, start, len, "dst"); \
        } else { \
            memcpy(data + start, buf, len * sizeof(_ctype)); \
        } \
    }

/*
 * 4-in-1:
 *  Get<Type>ArrayElements
 *  Release<Type>ArrayElements
 *  Get<Type>ArrayRegion
 *  Set<Type>ArrayRegion
 */
#define PRIMITIVE_ARRAY_FUNCTIONS(_ctype, _jname)                           \
    GET_PRIMITIVE_ARRAY_ELEMENTS(_ctype, _jname);                           \
    RELEASE_PRIMITIVE_ARRAY_ELEMENTS(_ctype, _jname);                       \
    GET_PRIMITIVE_ARRAY_REGION(_ctype, _jname);                             \
    SET_PRIMITIVE_ARRAY_REGION(_ctype, _jname);

PRIMITIVE_ARRAY_FUNCTIONS(jboolean, Boolean);
PRIMITIVE_ARRAY_FUNCTIONS(jbyte, Byte);
PRIMITIVE_ARRAY_FUNCTIONS(jchar, Char);
PRIMITIVE_ARRAY_FUNCTIONS(jshort, Short);
PRIMITIVE_ARRAY_FUNCTIONS(jint, Int);
PRIMITIVE_ARRAY_FUNCTIONS(jlong, Long);
PRIMITIVE_ARRAY_FUNCTIONS(jfloat, Float);
PRIMITIVE_ARRAY_FUNCTIONS(jdouble, Double);

/*
 * Register one or more native functions in one class.
 *
 * This can be called multiple times on the same method, allowing the
 * caller to redefine the method implementation at will.
 */
static jint RegisterNatives(JNIEnv* env, jclass jclazz,
    const JNINativeMethod* methods, jint nMethods)
{
    ScopedJniThreadState ts(env);

    ClassObject* clazz = (ClassObject*) dvmDecodeIndirectRef(env, jclazz);

    if (gDvm.verboseJni) {
        LOGI("[Registering JNI native methods for class %s]",
            clazz->descriptor);
    }

    for (int i = 0; i < nMethods; i++) {
        if (!dvmRegisterJNIMethod(clazz, methods[i].name,
                methods[i].signature, methods[i].fnPtr))
        {
            return JNI_ERR;
        }
    }
    return JNI_OK;
}

/*
 * Un-register all native methods associated with the class.
 *
 * The JNI docs refer to this as a way to reload/relink native libraries,
 * and say it "should not be used in normal native code".  In particular,
 * there is no need to do this during shutdown, and you do not need to do
 * this before redefining a method implementation with RegisterNatives.
 *
 * It's chiefly useful for a native "plugin"-style library that wasn't
 * loaded with System.loadLibrary() (since there's no way to unload those).
 * For example, the library could upgrade itself by:
 *
 *  1. call UnregisterNatives to unbind the old methods
 *  2. ensure that no code is still executing inside it (somehow)
 *  3. dlclose() the library
 *  4. dlopen() the new library
 *  5. use RegisterNatives to bind the methods from the new library
 *
 * The above can work correctly without the UnregisterNatives call, but
 * creates a window of opportunity in which somebody might try to call a
 * method that is pointing at unmapped memory, crashing the VM.  In theory
 * the same guards that prevent dlclose() from unmapping executing code could
 * prevent that anyway, but with this we can be more thorough and also deal
 * with methods that only exist in the old or new form of the library (maybe
 * the lib wants to try the call and catch the UnsatisfiedLinkError).
 */
static jint UnregisterNatives(JNIEnv* env, jclass jclazz) {
    ScopedJniThreadState ts(env);

    ClassObject* clazz = (ClassObject*) dvmDecodeIndirectRef(env, jclazz);
    if (gDvm.verboseJni) {
        LOGI("[Unregistering JNI native methods for class %s]",
            clazz->descriptor);
    }
    dvmUnregisterJNINativeMethods(clazz);
    return JNI_OK;
}

/*
 * Lock the monitor.
 *
 * We have to track all monitor enters and exits, so that we can undo any
 * outstanding synchronization before the thread exits.
 */
static jint MonitorEnter(JNIEnv* env, jobject jobj) {
    ScopedJniThreadState ts(env);
    Object* obj = dvmDecodeIndirectRef(env, jobj);
    dvmLockObject(ts.self(), obj);
    trackMonitorEnter(ts.self(), obj);
    return JNI_OK;
}

/*
 * Unlock the monitor.
 *
 * Throws an IllegalMonitorStateException if the current thread
 * doesn't own the monitor.  (dvmUnlockObject() takes care of the throw.)
 *
 * According to the 1.6 spec, it's legal to call here with an exception
 * pending.  If this fails, we'll stomp the original exception.
 */
static jint MonitorExit(JNIEnv* env, jobject jobj) {
    ScopedJniThreadState ts(env);
    Object* obj = dvmDecodeIndirectRef(env, jobj);
    bool success = dvmUnlockObject(ts.self(), obj);
    if (success) {
        trackMonitorExit(ts.self(), obj);
    }
    return success ? JNI_OK : JNI_ERR;
}

/*
 * Return the JavaVM interface associated with the current thread.
 */
static jint GetJavaVM(JNIEnv* env, JavaVM** vm) {
    ScopedJniThreadState ts(env);
    *vm = gDvmJni.jniVm;
    return (*vm == NULL) ? JNI_ERR : JNI_OK;
}

/*
 * Copies "len" Unicode characters, from offset "start".
 */
static void GetStringRegion(JNIEnv* env, jstring jstr, jsize start, jsize len, jchar* buf) {
    ScopedJniThreadState ts(env);
    StringObject* strObj = (StringObject*) dvmDecodeIndirectRef(env, jstr);
    int strLen = strObj->length();
    if (((start|len) < 0) || (start + len > strLen)) {
        dvmThrowStringIndexOutOfBoundsExceptionWithRegion(strLen, start, len);
        return;
    }
    memcpy(buf, strObj->chars() + start, len * sizeof(u2));
}

/*
 * Translates "len" Unicode characters, from offset "start", into
 * modified UTF-8 encoding.
 */
static void GetStringUTFRegion(JNIEnv* env, jstring jstr, jsize start, jsize len, char* buf) {
    ScopedJniThreadState ts(env);
    StringObject* strObj = (StringObject*) dvmDecodeIndirectRef(env, jstr);
    int strLen = strObj->length();
    if (((start|len) < 0) || (start + len > strLen)) {
        dvmThrowStringIndexOutOfBoundsExceptionWithRegion(strLen, start, len);
        return;
    }
    dvmGetStringUtfRegion(strObj, start, len, buf);
}

/*
 * Get a raw pointer to array data.
 *
 * The caller is expected to call "release" before doing any JNI calls
 * or blocking I/O operations.
 *
 * We need to pin the memory or block GC.
 */
static void* GetPrimitiveArrayCritical(JNIEnv* env, jarray jarr, jboolean* isCopy) {
    ScopedJniThreadState ts(env);
    ArrayObject* arrayObj = (ArrayObject*) dvmDecodeIndirectRef(env, jarr);
    pinPrimitiveArray(arrayObj);
    void* data = arrayObj->contents;
    if (isCopy != NULL) {
        *isCopy = JNI_FALSE;
    }
    return data;
}

/*
 * Release an array obtained with GetPrimitiveArrayCritical.
 */
static void ReleasePrimitiveArrayCritical(JNIEnv* env, jarray jarr, void* carray, jint mode) {
    if (mode != JNI_COMMIT) {
        ScopedJniThreadState ts(env);
        ArrayObject* arrayObj = (ArrayObject*) dvmDecodeIndirectRef(env, jarr);
        unpinPrimitiveArray(arrayObj);
    }
}

/*
 * Like GetStringChars, but with restricted use.
 */
static const jchar* GetStringCritical(JNIEnv* env, jstring jstr, jboolean* isCopy) {
    ScopedJniThreadState ts(env);

    StringObject* strObj = (StringObject*) dvmDecodeIndirectRef(env, jstr);
    ArrayObject* strChars = strObj->array();

    pinPrimitiveArray(strChars);

    const u2* data = strObj->chars();
    if (isCopy != NULL) {
        *isCopy = JNI_FALSE;
    }
    return (jchar*) data;
}

/*
 * Like ReleaseStringChars, but with restricted use.
 */
static void ReleaseStringCritical(JNIEnv* env, jstring jstr, const jchar* carray) {
    ScopedJniThreadState ts(env);
    StringObject* strObj = (StringObject*) dvmDecodeIndirectRef(env, jstr);
    ArrayObject* strChars = strObj->array();
    unpinPrimitiveArray(strChars);
}

/*
 * Create a new weak global reference.
 */
static jweak NewWeakGlobalRef(JNIEnv* env, jobject jobj) {
    ScopedJniThreadState ts(env);
    Object *obj = dvmDecodeIndirectRef(env, jobj);
    return (jweak) addWeakGlobalReference(obj);
}

/*
 * Delete the specified weak global reference.
 */
static void DeleteWeakGlobalRef(JNIEnv* env, jweak wref) {
    ScopedJniThreadState ts(env);
    deleteWeakGlobalReference(wref);
}

/*
 * Quick check for pending exceptions.
 *
 * TODO: we should be able to skip the enter/exit macros here.
 */
static jboolean ExceptionCheck(JNIEnv* env) {
    ScopedJniThreadState ts(env);
    return dvmCheckException(ts.self());
}

/*
 * Returns the type of the object referred to by "obj".  It can be local,
 * global, or weak global.
 *
 * In the current implementation, references can be global and local at
 * the same time, so while the return value is accurate it may not tell
 * the whole story.
 */
static jobjectRefType GetObjectRefType(JNIEnv* env, jobject jobj) {
    ScopedJniThreadState ts(env);
    return dvmGetJNIRefType(env, jobj);
}

/*
 * Allocate and return a new java.nio.ByteBuffer for this block of memory.
 *
 * "address" may not be NULL, and "capacity" must be > 0.  (These are only
 * verified when CheckJNI is enabled.)
 */
static jobject NewDirectByteBuffer(JNIEnv* env, void* address, jlong capacity) {
    ScopedJniThreadState ts(env);

    /* create an instance of java.nio.ReadWriteDirectByteBuffer */
    ClassObject* bufferClazz = gDvm.classJavaNioReadWriteDirectByteBuffer;
    if (!dvmIsClassInitialized(bufferClazz) && !dvmInitClass(bufferClazz)) {
        return NULL;
    }
    Object* newObj = dvmAllocObject(bufferClazz, ALLOC_DONT_TRACK);
    if (newObj == NULL) {
        return NULL;
    }
    /* call the constructor */
    jobject result = addLocalReference(env, newObj);
    JValue unused;
    dvmCallMethod(ts.self(), gDvm.methJavaNioReadWriteDirectByteBuffer_init,
            newObj, &unused, (jint) address, (jint) capacity);
    if (dvmGetException(ts.self()) != NULL) {
        deleteLocalReference(env, result);
        return NULL;
    }
    return result;
}

/*
 * Get the starting address of the buffer for the specified java.nio.Buffer.
 *
 * If this is not a "direct" buffer, we return NULL.
 */
static void* GetDirectBufferAddress(JNIEnv* env, jobject jbuf) {
    ScopedJniThreadState ts(env);

    // All Buffer objects have an effectiveDirectAddress field.
    Object* bufObj = dvmDecodeIndirectRef(env, jbuf);
    return (void*) dvmGetFieldInt(bufObj, gDvm.offJavaNioBuffer_effectiveDirectAddress);
}

/*
 * Get the capacity of the buffer for the specified java.nio.Buffer.
 *
 * Returns -1 if the object is not a direct buffer.  (We actually skip
 * this check, since it's expensive to determine, and just return the
 * capacity regardless.)
 */
static jlong GetDirectBufferCapacity(JNIEnv* env, jobject jbuf) {
    ScopedJniThreadState ts(env);

    /*
     * The capacity is always in the Buffer.capacity field.
     *
     * (The "check" version should verify that this is actually a Buffer,
     * but we're not required to do so here.)
     */
    Object* buf = dvmDecodeIndirectRef(env, jbuf);
    return dvmGetFieldInt(buf, gDvm.offJavaNioBuffer_capacity);
}


/*
 * ===========================================================================
 *      JNI invocation functions
 * ===========================================================================
 */

/*
 * Handle AttachCurrentThread{AsDaemon}.
 *
 * We need to make sure the VM is actually running.  For example, if we start
 * up, issue an Attach, and the VM exits almost immediately, by the time the
 * attaching happens the VM could already be shutting down.
 *
 * It's hard to avoid a race condition here because we don't want to hold
 * a lock across the entire operation.  What we can do is temporarily
 * increment the thread count to prevent a VM exit.
 *
 * This could potentially still have problems if a daemon thread calls here
 * while the VM is shutting down.  dvmThreadSelf() will work, since it just
 * uses pthread TLS, but dereferencing "vm" could fail.  Such is life when
 * you shut down a VM while threads are still running inside it.
 *
 * Remember that some code may call this as a way to find the per-thread
 * JNIEnv pointer.  Don't do excess work for that case.
 */
static jint attachThread(JavaVM* vm, JNIEnv** p_env, void* thr_args, bool isDaemon) {
    JavaVMAttachArgs* args = (JavaVMAttachArgs*) thr_args;

    /*
     * Return immediately if we're already one with the VM.
     */
    Thread* self = dvmThreadSelf();
    if (self != NULL) {
        *p_env = self->jniEnv;
        return JNI_OK;
    }

    /*
     * No threads allowed in zygote mode.
     */
    if (gDvm.zygote) {
        return JNI_ERR;
    }

    /* increment the count to keep the VM from bailing while we run */
    dvmLockThreadList(NULL);
    if (gDvm.nonDaemonThreadCount == 0) {
        // dead or dying
        LOGV("Refusing to attach thread '%s' -- VM is shutting down",
            (thr_args == NULL) ? "(unknown)" : args->name);
        dvmUnlockThreadList();
        return JNI_ERR;
    }
    gDvm.nonDaemonThreadCount++;
    dvmUnlockThreadList();

    /* tweak the JavaVMAttachArgs as needed */
    JavaVMAttachArgs argsCopy;
    if (args == NULL) {
        /* allow the v1.1 calling convention */
        argsCopy.version = JNI_VERSION_1_2;
        argsCopy.name = NULL;
        argsCopy.group = (jobject) dvmGetMainThreadGroup();
    } else {
        assert(args->version >= JNI_VERSION_1_2);

        argsCopy.version = args->version;
        argsCopy.name = args->name;
        if (args->group != NULL) {
            argsCopy.group = (jobject) dvmDecodeIndirectRef(NULL, args->group);
        } else {
            argsCopy.group = (jobject) dvmGetMainThreadGroup();
        }
    }

    bool result = dvmAttachCurrentThread(&argsCopy, isDaemon);

    /* restore the count */
    dvmLockThreadList(NULL);
    gDvm.nonDaemonThreadCount--;
    dvmUnlockThreadList();

    /*
     * Change the status to indicate that we're out in native code.  This
     * call is not guarded with state-change macros, so we have to do it
     * by hand.
     */
    if (result) {
        self = dvmThreadSelf();
        assert(self != NULL);
        dvmChangeStatus(self, THREAD_NATIVE);
        *p_env = self->jniEnv;
        return JNI_OK;
    } else {
        return JNI_ERR;
    }
}

/*
 * Attach the current thread to the VM.  If the thread is already attached,
 * this is a no-op.
 */
static jint AttachCurrentThread(JavaVM* vm, JNIEnv** p_env, void* thr_args) {
    return attachThread(vm, p_env, thr_args, false);
}

/*
 * Like AttachCurrentThread, but set the "daemon" flag.
 */
static jint AttachCurrentThreadAsDaemon(JavaVM* vm, JNIEnv** p_env, void* thr_args)
{
    return attachThread(vm, p_env, thr_args, true);
}

/*
 * Dissociate the current thread from the VM.
 */
static jint DetachCurrentThread(JavaVM* vm) {
    Thread* self = dvmThreadSelf();
    if (self == NULL) {
        /* not attached, can't do anything */
        return JNI_ERR;
    }

    /* switch to "running" to check for suspension */
    dvmChangeStatus(self, THREAD_RUNNING);

    /* detach the thread */
    dvmDetachCurrentThread();

    /* (no need to change status back -- we have no status) */
    return JNI_OK;
}

/*
 * If current thread is attached to VM, return the associated JNIEnv.
 * Otherwise, stuff NULL in and return JNI_EDETACHED.
 *
 * JVMTI overloads this by specifying a magic value for "version", so we
 * do want to check that here.
 */
static jint GetEnv(JavaVM* vm, void** env, jint version) {
    Thread* self = dvmThreadSelf();

    if (version < JNI_VERSION_1_1 || version > JNI_VERSION_1_6) {
        return JNI_EVERSION;
    }

    if (self == NULL) {
        *env = NULL;
    } else {
        /* TODO: status change is probably unnecessary */
        dvmChangeStatus(self, THREAD_RUNNING);
        *env = (void*) dvmGetThreadJNIEnv(self);
        dvmChangeStatus(self, THREAD_NATIVE);
    }
    return (*env != NULL) ? JNI_OK : JNI_EDETACHED;
}

/*
 * Destroy the VM.  This may be called from any thread.
 *
 * If the current thread is attached, wait until the current thread is
 * the only non-daemon user-level thread.  If the current thread is not
 * attached, we attach it and do the processing as usual.  (If the attach
 * fails, it's probably because all the non-daemon threads have already
 * exited and the VM doesn't want to let us back in.)
 *
 * TODO: we don't really deal with the situation where more than one thread
 * has called here.  One thread wins, the other stays trapped waiting on
 * the condition variable forever.  Not sure this situation is interesting
 * in real life.
 */
static jint DestroyJavaVM(JavaVM* vm) {
    JavaVMExt* ext = (JavaVMExt*) vm;
    if (ext == NULL) {
        return JNI_ERR;
    }

    if (gDvm.verboseShutdown) {
        LOGD("DestroyJavaVM waiting for non-daemon threads to exit");
    }

    /*
     * Sleep on a condition variable until it's okay to exit.
     */
    Thread* self = dvmThreadSelf();
    if (self == NULL) {
        JNIEnv* tmpEnv;
        if (AttachCurrentThread(vm, &tmpEnv, NULL) != JNI_OK) {
            LOGV("Unable to reattach main for Destroy; assuming VM is shutting down (count=%d)",
                gDvm.nonDaemonThreadCount);
            goto shutdown;
        } else {
            LOGV("Attached to wait for shutdown in Destroy");
        }
    }
    dvmChangeStatus(self, THREAD_VMWAIT);

    dvmLockThreadList(self);
    gDvm.nonDaemonThreadCount--;    // remove current thread from count

    while (gDvm.nonDaemonThreadCount > 0) {
        pthread_cond_wait(&gDvm.vmExitCond, &gDvm.threadListLock);
    }

    dvmUnlockThreadList();
    self = NULL;

shutdown:
    // TODO: call System.exit() to run any registered shutdown hooks
    // (this may not return -- figure out how this should work)

    if (gDvm.verboseShutdown) {
        LOGD("DestroyJavaVM shutting VM down");
    }
    dvmShutdown();

    // TODO - free resources associated with JNI-attached daemon threads
    free(ext->envList);
    free(ext);

    return JNI_OK;
}


/*
 * ===========================================================================
 *      Function tables
 * ===========================================================================
 */

static const struct JNINativeInterface gNativeInterface = {
    NULL,
    NULL,
    NULL,
    NULL,

    GetVersion,

    DefineClass,
    FindClass,

    FromReflectedMethod,
    FromReflectedField,
    ToReflectedMethod,

    GetSuperclass,
    IsAssignableFrom,

    ToReflectedField,

    Throw,
    ThrowNew,
    ExceptionOccurred,
    ExceptionDescribe,
    ExceptionClear,
    FatalError,

    PushLocalFrame,
    PopLocalFrame,

    NewGlobalRef,
    DeleteGlobalRef,
    DeleteLocalRef,
    IsSameObject,
    NewLocalRef,
    EnsureLocalCapacity,

    AllocObject,
    NewObject,
    NewObjectV,
    NewObjectA,

    GetObjectClass,
    IsInstanceOf,

    GetMethodID,

    CallObjectMethod,
    CallObjectMethodV,
    CallObjectMethodA,
    CallBooleanMethod,
    CallBooleanMethodV,
    CallBooleanMethodA,
    CallByteMethod,
    CallByteMethodV,
    CallByteMethodA,
    CallCharMethod,
    CallCharMethodV,
    CallCharMethodA,
    CallShortMethod,
    CallShortMethodV,
    CallShortMethodA,
    CallIntMethod,
    CallIntMethodV,
    CallIntMethodA,
    CallLongMethod,
    CallLongMethodV,
    CallLongMethodA,
    CallFloatMethod,
    CallFloatMethodV,
    CallFloatMethodA,
    CallDoubleMethod,
    CallDoubleMethodV,
    CallDoubleMethodA,
    CallVoidMethod,
    CallVoidMethodV,
    CallVoidMethodA,

    CallNonvirtualObjectMethod,
    CallNonvirtualObjectMethodV,
    CallNonvirtualObjectMethodA,
    CallNonvirtualBooleanMethod,
    CallNonvirtualBooleanMethodV,
    CallNonvirtualBooleanMethodA,
    CallNonvirtualByteMethod,
    CallNonvirtualByteMethodV,
    CallNonvirtualByteMethodA,
    CallNonvirtualCharMethod,
    CallNonvirtualCharMethodV,
    CallNonvirtualCharMethodA,
    CallNonvirtualShortMethod,
    CallNonvirtualShortMethodV,
    CallNonvirtualShortMethodA,
    CallNonvirtualIntMethod,
    CallNonvirtualIntMethodV,
    CallNonvirtualIntMethodA,
    CallNonvirtualLongMethod,
    CallNonvirtualLongMethodV,
    CallNonvirtualLongMethodA,
    CallNonvirtualFloatMethod,
    CallNonvirtualFloatMethodV,
    CallNonvirtualFloatMethodA,
    CallNonvirtualDoubleMethod,
    CallNonvirtualDoubleMethodV,
    CallNonvirtualDoubleMethodA,
    CallNonvirtualVoidMethod,
    CallNonvirtualVoidMethodV,
    CallNonvirtualVoidMethodA,

    GetFieldID,

    GetObjectField,
    GetBooleanField,
    GetByteField,
    GetCharField,
    GetShortField,
    GetIntField,
    GetLongField,
    GetFloatField,
    GetDoubleField,
    SetObjectField,
    SetBooleanField,
    SetByteField,
    SetCharField,
    SetShortField,
    SetIntField,
    SetLongField,
    SetFloatField,
    SetDoubleField,

    GetStaticMethodID,

    CallStaticObjectMethod,
    CallStaticObjectMethodV,
    CallStaticObjectMethodA,
    CallStaticBooleanMethod,
    CallStaticBooleanMethodV,
    CallStaticBooleanMethodA,
    CallStaticByteMethod,
    CallStaticByteMethodV,
    CallStaticByteMethodA,
    CallStaticCharMethod,
    CallStaticCharMethodV,
    CallStaticCharMethodA,
    CallStaticShortMethod,
    CallStaticShortMethodV,
    CallStaticShortMethodA,
    CallStaticIntMethod,
    CallStaticIntMethodV,
    CallStaticIntMethodA,
    CallStaticLongMethod,
    CallStaticLongMethodV,
    CallStaticLongMethodA,
    CallStaticFloatMethod,
    CallStaticFloatMethodV,
    CallStaticFloatMethodA,
    CallStaticDoubleMethod,
    CallStaticDoubleMethodV,
    CallStaticDoubleMethodA,
    CallStaticVoidMethod,
    CallStaticVoidMethodV,
    CallStaticVoidMethodA,

    GetStaticFieldID,

    GetStaticObjectField,
    GetStaticBooleanField,
    GetStaticByteField,
    GetStaticCharField,
    GetStaticShortField,
    GetStaticIntField,
    GetStaticLongField,
    GetStaticFloatField,
    GetStaticDoubleField,

    SetStaticObjectField,
    SetStaticBooleanField,
    SetStaticByteField,
    SetStaticCharField,
    SetStaticShortField,
    SetStaticIntField,
    SetStaticLongField,
    SetStaticFloatField,
    SetStaticDoubleField,

    NewString,

    GetStringLength,
    GetStringChars,
    ReleaseStringChars,

    NewStringUTF,
    GetStringUTFLength,
    GetStringUTFChars,
    ReleaseStringUTFChars,

    GetArrayLength,
    NewObjectArray,
    GetObjectArrayElement,
    SetObjectArrayElement,

    NewBooleanArray,
    NewByteArray,
    NewCharArray,
    NewShortArray,
    NewIntArray,
    NewLongArray,
    NewFloatArray,
    NewDoubleArray,

    GetBooleanArrayElements,
    GetByteArrayElements,
    GetCharArrayElements,
    GetShortArrayElements,
    GetIntArrayElements,
    GetLongArrayElements,
    GetFloatArrayElements,
    GetDoubleArrayElements,

    ReleaseBooleanArrayElements,
    ReleaseByteArrayElements,
    ReleaseCharArrayElements,
    ReleaseShortArrayElements,
    ReleaseIntArrayElements,
    ReleaseLongArrayElements,
    ReleaseFloatArrayElements,
    ReleaseDoubleArrayElements,

    GetBooleanArrayRegion,
    GetByteArrayRegion,
    GetCharArrayRegion,
    GetShortArrayRegion,
    GetIntArrayRegion,
    GetLongArrayRegion,
    GetFloatArrayRegion,
    GetDoubleArrayRegion,
    SetBooleanArrayRegion,
    SetByteArrayRegion,
    SetCharArrayRegion,
    SetShortArrayRegion,
    SetIntArrayRegion,
    SetLongArrayRegion,
    SetFloatArrayRegion,
    SetDoubleArrayRegion,

    RegisterNatives,
    UnregisterNatives,

    MonitorEnter,
    MonitorExit,

    GetJavaVM,

    GetStringRegion,
    GetStringUTFRegion,

    GetPrimitiveArrayCritical,
    ReleasePrimitiveArrayCritical,

    GetStringCritical,
    ReleaseStringCritical,

    NewWeakGlobalRef,
    DeleteWeakGlobalRef,

    ExceptionCheck,

    NewDirectByteBuffer,
    GetDirectBufferAddress,
    GetDirectBufferCapacity,

    GetObjectRefType
};

static const struct JNIInvokeInterface gInvokeInterface = {
    NULL,
    NULL,
    NULL,

    DestroyJavaVM,
    AttachCurrentThread,
    DetachCurrentThread,

    GetEnv,

    AttachCurrentThreadAsDaemon,
};

/*
 * ===========================================================================
 *      VM/Env creation
 * ===========================================================================
 */

/*
 * Create a new JNIEnv struct and add it to the VM's list.
 *
 * "self" will be NULL for the main thread, since the VM hasn't started
 * yet; the value will be filled in later.
 */
JNIEnv* dvmCreateJNIEnv(Thread* self) {
    JavaVMExt* vm = (JavaVMExt*) gDvmJni.jniVm;

    //if (self != NULL)
    //    LOGI("Ent CreateJNIEnv: threadid=%d %p", self->threadId, self);

    assert(vm != NULL);

    JNIEnvExt* newEnv = (JNIEnvExt*) calloc(1, sizeof(JNIEnvExt));
    newEnv->funcTable = &gNativeInterface;
    if (self != NULL) {
        dvmSetJniEnvThreadId((JNIEnv*) newEnv, self);
        assert(newEnv->envThreadId != 0);
    } else {
        /* make it obvious if we fail to initialize these later */
        newEnv->envThreadId = 0x77777775;
        newEnv->self = (Thread*) 0x77777779;
    }
    if (gDvmJni.useCheckJni) {
        dvmUseCheckedJniEnv(newEnv);
    }

    ScopedPthreadMutexLock lock(&vm->envListLock);

    /* insert at head of list */
    newEnv->next = vm->envList;
    assert(newEnv->prev == NULL);
    if (vm->envList == NULL) {
        // rare, but possible
        vm->envList = newEnv;
    } else {
        vm->envList->prev = newEnv;
    }
    vm->envList = newEnv;

    //if (self != NULL)
    //    LOGI("Xit CreateJNIEnv: threadid=%d %p", self->threadId, self);
    return (JNIEnv*) newEnv;
}

/*
 * Remove a JNIEnv struct from the list and free it.
 */
void dvmDestroyJNIEnv(JNIEnv* env) {
    if (env == NULL) {
        return;
    }

    //LOGI("Ent DestroyJNIEnv: threadid=%d %p", self->threadId, self);

    JNIEnvExt* extEnv = (JNIEnvExt*) env;
    JavaVMExt* vm = (JavaVMExt*) gDvmJni.jniVm;

    ScopedPthreadMutexLock lock(&vm->envListLock);

    if (extEnv == vm->envList) {
        assert(extEnv->prev == NULL);
        vm->envList = extEnv->next;
    } else {
        assert(extEnv->prev != NULL);
        extEnv->prev->next = extEnv->next;
    }
    if (extEnv->next != NULL) {
        extEnv->next->prev = extEnv->prev;
    }

    free(env);
    //LOGI("Xit DestroyJNIEnv: threadid=%d %p", self->threadId, self);
}

/*
 * Enable "checked JNI" after the VM has partially started.  This must
 * only be called in "zygote" mode, when we have one thread running.
 *
 * This doesn't attempt to rewrite the JNI call bridge associated with
 * native methods, so we won't get those checks for any methods that have
 * already been resolved.
 */
void dvmLateEnableCheckedJni() {
    JNIEnvExt* extEnv = dvmGetJNIEnvForThread();
    if (extEnv == NULL) {
        LOGE("dvmLateEnableCheckedJni: thread has no JNIEnv");
        return;
    }
    JavaVMExt* extVm = (JavaVMExt*) gDvmJni.jniVm;
    assert(extVm != NULL);

    if (!gDvmJni.useCheckJni) {
        LOGD("Late-enabling CheckJNI");
        dvmUseCheckedJniVm(extVm);
        dvmUseCheckedJniEnv(extEnv);
    } else {
        LOGD("Not late-enabling CheckJNI (already on)");
    }
}

/*
 * Not supported.
 */
jint JNI_GetDefaultJavaVMInitArgs(void* vm_args) {
    return JNI_ERR;
}

/*
 * Return a buffer full of created VMs.
 *
 * We always have zero or one.
 */
jint JNI_GetCreatedJavaVMs(JavaVM** vmBuf, jsize bufLen, jsize* nVMs) {
    if (gDvmJni.jniVm != NULL) {
        *nVMs = 1;
        if (bufLen > 0) {
            *vmBuf++ = gDvmJni.jniVm;
        }
    } else {
        *nVMs = 0;
    }
    return JNI_OK;
}

/*
 * Create a new VM instance.
 *
 * The current thread becomes the main VM thread.  We return immediately,
 * which effectively means the caller is executing in a native method.
 */
jint JNI_CreateJavaVM(JavaVM** p_vm, JNIEnv** p_env, void* vm_args) {
    const JavaVMInitArgs* args = (JavaVMInitArgs*) vm_args;
    if (args->version < JNI_VERSION_1_2) {
        return JNI_EVERSION;
    }

    // TODO: don't allow creation of multiple VMs -- one per customer for now

    /* zero globals; not strictly necessary the first time a VM is started */
    memset(&gDvm, 0, sizeof(gDvm));

    /*
     * Set up structures for JNIEnv and VM.
     */
    JavaVMExt* pVM = (JavaVMExt*) malloc(sizeof(JavaVMExt));
    memset(pVM, 0, sizeof(JavaVMExt));
    pVM->funcTable = &gInvokeInterface;
    pVM->envList = NULL;
    dvmInitMutex(&pVM->envListLock);

    UniquePtr<const char*[]> argv(new const char*[args->nOptions]);
    memset(argv.get(), 0, sizeof(char*) * (args->nOptions));

    /*
     * Convert JNI args to argv.
     *
     * We have to pull out vfprintf/exit/abort, because they use the
     * "extraInfo" field to pass function pointer "hooks" in.  We also
     * look for the -Xcheck:jni stuff here.
     */
    int argc = 0;
    for (int i = 0; i < args->nOptions; i++) {
        const char* optStr = args->options[i].optionString;
        if (optStr == NULL) {
            dvmFprintf(stderr, "ERROR: CreateJavaVM failed: argument %d was NULL\n", i);
            return JNI_ERR;
        } else if (strcmp(optStr, "vfprintf") == 0) {
            gDvm.vfprintfHook = (int (*)(FILE *, const char*, va_list))args->options[i].extraInfo;
        } else if (strcmp(optStr, "exit") == 0) {
            gDvm.exitHook = (void (*)(int)) args->options[i].extraInfo;
        } else if (strcmp(optStr, "abort") == 0) {
            gDvm.abortHook = (void (*)(void))args->options[i].extraInfo;
        } else if (strcmp(optStr, "sensitiveThread") == 0) {
            gDvm.isSensitiveThreadHook = (bool (*)(void))args->options[i].extraInfo;
        } else if (strcmp(optStr, "-Xcheck:jni") == 0) {
            gDvmJni.useCheckJni = true;
        } else if (strncmp(optStr, "-Xjniopts:", 10) == 0) {
            char* jniOpts = strdup(optStr + 10);
            size_t jniOptCount = 1;
            for (char* p = jniOpts; *p != 0; ++p) {
                if (*p == ',') {
                    ++jniOptCount;
                    *p = 0;
                }
            }
            char* jniOpt = jniOpts;
            for (size_t i = 0; i < jniOptCount; ++i) {
                if (strcmp(jniOpt, "warnonly") == 0) {
                    gDvmJni.warnOnly = true;
                } else if (strcmp(jniOpt, "forcecopy") == 0) {
                    gDvmJni.forceCopy = true;
                } else if (strcmp(jniOpt, "logThirdPartyJni") == 0) {
                    gDvmJni.logThirdPartyJni = true;
                } else {
                    dvmFprintf(stderr, "ERROR: CreateJavaVM failed: unknown -Xjniopts option '%s'\n",
                            jniOpt);
                    return JNI_ERR;
                }
                jniOpt += strlen(jniOpt) + 1;
            }
            free(jniOpts);
        } else {
            /* regular option */
            argv[argc++] = optStr;
        }
    }

    if (gDvmJni.useCheckJni) {
        dvmUseCheckedJniVm(pVM);
    }

    if (gDvmJni.jniVm != NULL) {
        dvmFprintf(stderr, "ERROR: Dalvik only supports one VM per process\n");
        return JNI_ERR;
    }
    gDvmJni.jniVm = (JavaVM*) pVM;

    /*
     * Create a JNIEnv for the main thread.  We need to have something set up
     * here because some of the class initialization we do when starting
     * up the VM will call into native code.
     */
    JNIEnvExt* pEnv = (JNIEnvExt*) dvmCreateJNIEnv(NULL);

    /* Initialize VM. */
    gDvm.initializing = true;
    std::string status =
            dvmStartup(argc, argv.get(), args->ignoreUnrecognized, (JNIEnv*)pEnv);
    gDvm.initializing = false;

    if (!status.empty()) {
        free(pEnv);
        free(pVM);
        LOGW("CreateJavaVM failed: %s", status.c_str());
        return JNI_ERR;
    }

    /*
     * Success!  Return stuff to caller.
     */
    dvmChangeStatus(NULL, THREAD_NATIVE);
    *p_env = (JNIEnv*) pEnv;
    *p_vm = (JavaVM*) pVM;
    LOGV("CreateJavaVM succeeded");
    return JNI_OK;
}