static jobject android_os_Parcel_readStrongBinder(JNIEnv* env, jclass clazz, jint nativePtr)
{
    Parcel* parcel = reinterpret_cast<Parcel*>(nativePtr);
    if (parcel != NULL) {
        return javaObjectForIBinder(env, parcel->readStrongBinder());
    }
    return NULL;
}

sp<IBinder> Parcel::readStrongBinder() const {
    sp<IBinder> val;
    unflatten_binder(ProcessState::self(), *this, &val);
    return val;
}

status_t unflatten_binder(const sp<ProcessState>& proc, const Parcel& in, sp<IBinder>* out) {
    const flat_binder_object* flat = in.readObject(false);    
    if (flat) {
        switch (flat->type) {
            case BINDER_TYPE_BINDER:
                *out = static_cast<IBinder*>(flat->cookie);
                return finish_unflatten_binder(NULL, *flat, in);
            case BINDER_TYPE_HANDLE:
                *out = proc->getStrongProxyForHandle(flat->handle);
                return finish_unflatten_binder(
                    static_cast<BpBinder*>(out->get()), *flat, in);
        }        
}

如果是同一进程，那么将返回一个JavaBBinder对象；如果是跨进程将进入getStrongProxyForHandle。

sp<IBinder> ProcessState::getStrongProxyForHandle(int32_t handle) {
    sp<IBinder> result;
    AutoMutex _l(mLock);
    handle_entry* e = lookupHandleLocked(handle);
    if (e != NULL) {
        IBinder* b = e->binder;
        if (b == NULL || !e->refs->attemptIncWeak(this)) {
            if (handle == 0) {
                Parcel data;
                status_t status = IPCThreadState::self()->transact(
                        0, IBinder::PING_TRANSACTION, data, NULL, 0);
                if (status == DEAD_OBJECT)
                   return NULL;
            }
            b = new BpBinder(handle); 
            e->binder = b;
            if (b) e->refs = b->getWeakRefs();
            result = b;
        } else {
            result.force_set(b);
            e->refs->decWeak(this);
        }
    }
    return result;
}

返回一个BpBinder对象，接着请查看javaObjectForIBinder方法。