The ExoVM system for automatic VM and application reduction

This paper describes how virtual classes can be supported in a vir-tual machine. Main-stream virtual machines such as the Java Vir-tual Machine and the.NET platform dominate the world today, and many languages are being executed on these virtual machines even though their embodied design choices conflict with the design choices of the virtual machine. For instance, there is a non-trivial mismatch between the main-stream virtual machines mentioned above and dynamically typed languages. One language concept that creates an even greater mismatch is virtual classes, in particular be-cause fully general support for virtual classes requires generation of new classes at run-time by mixin composition. Languages like CaesarJ and Object Teams can express virtual classes restricted to the subset that does not require run-time generation of classes, be-cause of the restrictions imposed by the Java Virtual Machine. We have chosen to support virtual classes by implementing a special-ized virtual machine, and this paper describes how this virtual ma-chine supports virtual classes with full generality.

In this paper we develop a model which represents the addressing of resources by processes executing on a virtual machine. The model distinguishes two maps: the o-map which represents the map visible to the operating system software running on the virtual machine, and the f-map which is invisible to that software but which is manipulated by the virtual machine monitor running on the real machine. The o-map maps process names into resource names and the f-map maps virtual resource names into real resource names. Thus, a process running on a virtual machine addresses its resources under the composed map f o o. In recursive operation, f maps from one virtual machine level to another and we have f o f o ... o f o o.The model is used to describe and characterize previous virtual machine designs. We also introduce and illustrate a general approach for implementing virtual machines which follows directly from the model. This design, the Hardware Virtualizer, handles all process exceptions directly within the executing virtual machine without software intervention. All resource faults (VM-faults) generated by a virtual machine are directed to the appropriate virtual machine monitor without the knowledge of processes on the virtual machine (regardless of the level of recursion).

Hardware/software co-design and (re)configurable computing with field programmable gate arrays (FPGAs) are used to create a highly efficient implementation of the Java virtual machine (JVM). Guidelines are provided for applying a general hardware/software co-design process to virtual machines, as are algorithms for context switching between the hardware and software partitions. The advantages of using co-design as an implementation approach for virtual machines are assessed using several benchmarks applied to the implemented co-design of the JVM. It is shown that significant performance improvements are achievable with appropriate architectural and co-design choices. The co-designed JVM could be a cost-effective solution for use in situations where the usual methods of virtual machine acceleration are inappropriate.

Object oriented software design is getting more and more common in the field of industrial control. In particular, Java seems extremely versatile for the development of distributed control applications. One of the main requirements of control application is a deterministic execution of the tasks, which generally feature real-time constraints. When Java language has been conceived, a little weight to the real-time requirements of applications has been given. In the last few years the limits to the use of Java for real-time applications has led to the definition of Java Real-Time platform specifications. Real-time capability of a Java virtual machine (VM) depends on a very large number of elements, among which the task scheduling algorithm, the memory management, the garbage collector algorithm and its execution policy. Knowledge of how each single internal mechanism of a Java VM influence its performance is very important to improve its real-time behaviour. This paper must be considered as a first step toward this direction, as its aim is to try to understand how real-time performance of a Java VM may be influenced by each its single component.

Virtual machines raise the abstraction level of the execution environment at the cost of restricting the set of supported languages. Moreover, the ability of a language implementation to integrate with other languages hosted on the same virtual machine typically constrains the features of the language. In this paper, we present a highly flexible yet efficient approach to hosting multiple programming languages on an objectoriented virtual machine. Our approach is based on extending the interface of each class with language-specific wrapper methods, offering each language a tailored view of a given class. This approach can be deployed both on a statically typed virtual machine, such as the JVM, and on a dynamic virtual machine, such as a Smalltalk virtual machine. We have implemented our approach to language interoperability on top of a prototype virtual machine for embedded systems based on the Smalltalk object model, which provides interoperability for embedded versions of the Smalltalk, Java, and BETA programming languages. (Less)

This paper describes how virtual classes can be supported in a virtual machine. Main-stream virtual machines such as the Java Virtual Machine and the .NET platform dominate the world today, and many languages are being executed on these virtual machines ...

Safepoints are a virtual machine mechanism that allows one thread to suspend other threads in a known state so that runtime actions can be performed without interruption and with data structures in a consistent state. Many virtual machines use safepoints as a mechanism to provide services such as stop-the-world garbage collection, debugging, and modification to running code such as installing or replacing classes. Languages implemented on these virtual machines may have access to these services, but not directly to the safepoint mechanism itself. We show that safepoints have many useful applications for the implementation of guest languages running on a virtual machine. We describe an API for using safepoints in languages that were implemented under the Truffle language implementation framework on the Java Virtual Machine and show several applications of the API to implement useful guest-language functionality. We present an efficient implementation of this API, when running in combination with the Graal dynamic compiler. We also demonstrate that our safepoints cause zero overhead with respect to peak performance and statistically insignificant overhead with respect to compilation time. We compare this to other techniques that could be used to implement the same functionality and demonstrate the large overhead that they incur.

Array is an important feature in Java and Java Virtual Machine. In spite of its importance, it has not been modeled by any existing Java Virtual Machine Models. In this paper, we define an extending model which uses an existing model as a basis and give the hierarchy of these two models, to model the array. In the extending model, we model the array in three steps. The first step is adding array related instructions in a formal way. The second step is refining the type compatibility to include array types. The last step is implementing array loading process also in a formal way. In the last part of thesis, we give the future work of extending other important features in Java and Java Virtual Machine.

From experience with wireless sensor networks it has become apparent that dynamic reprogramming of the sensor nodes is a useful feature. The resource constraints in terms of energy, memory, and processing power make sensor network reprogramming a challenging task. Many different mechanisms for reprogramming sensor nodes have been developed ranging from full image replacement to virtual machines.We have implemented an in-situ run-time dynamic linker and loader that use the standard ELF object file format. We show that run-time dynamic linking is an effective method for reprogramming even resource constrained wireless sensor nodes. To evaluate our dynamic linking mechanism we have implemented an application-specific virtual machine and a Java virtual machine and compare the energy cost of the different linking and execution models. We measure the energy consumption and execution time overhead on real hardware to quantify the energy costs for dynamic linkin.Our results suggest that while in general the overhead of a virtual machine is high, a combination of native code and virtual machine code provide good energy efficiency. Dynamic run-time linking can be used to update the native code, even in heterogeneous networks.

Scala is a new programming language developed at EPFL and incorporating the most important concepts of object-oriented and functional languages. It aims at integrating well with the Java and .NET platforms: their respective libraries are accessible without glue code, and the compiler can produce programs for both virtual machines. This thesis focuses on the compilation of two important concepts of Scala : mixin inheritance and run time types. The compilation techniques are presented in the context of the Java virtual machine, but could be adapted easily to other similar environments. Mixin inheritance is a relatively recent form of inheritance, offering new capabilities compared to single inheritance, without the complexity of multiple inheritance. We propose two implementation techniques for mixin inheritance: code copying and delegation. The implementation used in the Scala compiler is then presented and justified. Run time types make it possible for a program to examine the type of its values during execution. This possibility is interesting in itself, offering new capabilities to the programmer. Furthermore, run time types are also required to implement other high level concepts, like pattern matching, type-safe serialisation and reflection. We propose an implementation technique based on the representation of types as values, and show how to use the run time types of the underlying virtual machine to implement those of Scala. The techniques presented in this thesis have been implemented in our Scala compiler, scalac. This enabled us to evaluate these techniques, in particular their impact on the performances of programs. This evaluation was performed on several real, non-trivial programs.

Superblock compilation techniques such as control flow graph (CFG) or trace compilation have become a widely adopted approach to increase the performance of dynamically compiling virtual machines even further. While this was shown to be successful for many conventional virtual machines, it did not result in a higher performance for Java-based DBT machine emulators so far. These emulators dynamically translate application binaries of a target machine into Java bytecode, which is then eventually compiled into the native code of the emulating host by the Java Virtual Machine (JVM). Successful superblock compilation techniques for this class of emulators must consider the special requirements that result from the two-stage translation as well as the characteristics of the JVM, such as the inability of most Java JIT compilers to handle large bytecode methods efficiently. In this paper, we present a superblock compilation approach for a Java-based DBT machine emulator that generates a performance increase of up to 90 percent and of 32 percent on average. The key idea of our design is to provide a large scope over the control flow of target applications across basic block boundaries for the JVM, while still keeping small bytecode methods for the execution units. In addition, we also present two further optimizations -- interpreter context elimination and program counter elimination -- which increase the emulation performance by 16 percent again. In total, the optimization techniques discussed in this paper provide an average performance gain of 48 percent for the surveyed emulator.

Just-in-time (JIT) compilation during program execution and ahead-of-time (AOT) compilation during software installation are alternate techniques used by managed language virtual machines (VM) to generate optimized native code while simultaneously achieving binary code portability and high execution performance. Profile data collected by JIT compilers at run-time can enable profile-guided optimizations (PGO) to customize the generated native code to different program inputs. AOT compilation removes the speed and energy overhead of online profile collection and dynamic compilation, but may not be able to achieve the quality and performance of customized native code. The goal of this work is to investigate and quantify the implications of the AOT compilation model on the quality of the generated native code for current VMs. First, we quantify the quality of native code generated by the two compilation models for a state-of-the-art (HotSpot) Java VM. Second, we determine how the amount of profile data collected affects the quality of generated code. Third, we develop a mechanism to determine the accuracy or similarity for different profile data for a given program run, and investigate how the accuracy of profile data affects its ability to effectively guide PGOs. Finally, we categorize the profile data types in our VM and explore the contribution of each such category to performance.

While cloud customers can benefit from migrating applications to the cloud, they are concerned about the security of the hosted applications. This is complicated by the customers not knowing whether their cloud applications are working as expected. Although memory-safety Java Virtual Machine (JVM) can alleviate their anxiety due to the control flow integrity, their applications are prone to a violation of bytecode integrity. The analysis of some Java exploits indicates that the violation results primarily from the given excess sandbox permission, loading flaws in Java class libraries and third-party middlewares and the abuse of sun.misc.UnsafeAPI. To such an end, we design an architecture, called RIM4J, to enforce a runtime integrity measurement of Java bytecode within a cloud system, with the ability to attest this to a cloud customer in an unforgeable manner. Our RIM4J architecture is portable, such that it can be quickly deployed and adopted for real-world purposes, without requiring modifications to the underlying systems and access to application source code. Moreover, our RIM4J architecture is the first to measure dynamically-generated bytecode. We apply our runtime measurement architecture to a messaging server application where we show how RIM4J can detect undesirable behaviors, such as uploading arbitrary files and remote code execution. This paper also reports the experimental evaluation of a RIM4J prototype using both a macro- and a micro-benchmark; the experimental results indicate that RIM4J is a practical solution for real-world applications.

Application migration and heterogeneity are inherent issues of pervasive systems. Each implementation of a pervasive system must provide its own migration framework which hides heterogeneity of the different resources. This leads to the development of many frameworks that perform the same functionality. We propose a minimal execution environment, the micro virtual machine, that factorizes process migration implementation and offers heterogeneity, transparency and performance. Systems implemented on top of this micro virtual machine, such as our own Java virtual machine, will therefore automatically inherit process migration capabilities.KeywordsVirtual MachineDestination NodeProcess MigrationExecution EnvironmentProgram CounterThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Wireless Sensor Networks (WSN) have become highly attractive subject among researchers due to its wide area of uses. Developing applications for sensor nodes still remain a cumbersome task due to issues such as its heterogeneous nature, lack of low-level abstractions and lack of proper programming interfaces. To solve these issues, different Virtual Machines (VM) have been proposed to be used as middleware. A VM can be application specific in nature which supports instructions that directly addresses the domain specific problem or it can be general purpose which supports general programming instructions. This research work studies the possibility of adding concepts of application specific virtual machine to general purpose one. We have attempted to do so by providing a single bytecode implementation for some methods that are used frequently in WSN applications. To test our approach we have decided to use an existing Java Virtual Machine (JVM) implementation for WSN platform. The result is significant decrease in application binary size.