Java Bytecode Research Articles

Parallel execution of Java loops on Graphics Processing Units

Accelerated graphics cards, or Graphics Processing Units (GPUs), have become ubiquitous in recent years. On the right kinds of problems, GPUs greatly surpass CPUs in terms of raw performance. However, because they are difficult to program, GPUs are used only for a narrow class of special-purpose applications; the raw processing power made available by GPUs is unused most of the time.This paper presents an extension to a Java JIT compiler that executes suitable code on the GPU instead of the CPU. Both static and dynamic features are used to decide whether it is feasible and beneficial to off-load a piece of code on the GPU. The paper presents a cost model that balances the speedup available from the GPU against the cost of transferring input and output data between main memory and GPU memory. The cost model is parameterized so that it can be applied to different hardware combinations. The paper also presents ways to overcome several obstacles to parallelization inherent in the design of the Java bytecode language: unstructured control flow, the lack of multi-dimensional arrays, the precise exception semantics, and the proliferation of indirect references.

SAT-based termination analysis using monotonicity constraints over the integers

AbstractWe describe an algorithm for proving termination of programs abstracted to systems of monotonicity constraints in the integer domain. Monotonicity constraints are a nontrivial extension of the well-known size-change termination method. While deciding termination for systems of monotonicity constraints is PSPACE complete, we focus on a well-defined and significant subset, which we call MCNP (for “monotonicity constraints in NP”), designed to be amenable to a SAT-based solution. Our technique is based on the search for a special type of ranking function defined in terms of bounded differences between multisets of integer values. We describe the application of our approach as the back end for the termination analysis of Java Bytecode. At the front end, systems of monotonicity constraints are obtained by abstracting information, using two different termination analyzers:AProVEandCOSTA. Preliminary results reveal that our approach provides a good trade-off between precision and cost of analysis.

Amortised Resource Analysis with Separation Logic

Type-based amortised resource analysis following Hofmann and Jost---where resources are associated with individual elements of data structures and doled out to the programmer under a linear typing discipline---have been successful in providing concrete resource bounds for functional programs, with good support for inference. In this work we translate the idea of amortised resource analysis to imperative pointer-manipulating languages by embedding a logic of resources, based on the affine intuitionistic Logic of Bunched Implications, within Separation Logic. The Separation Logic component allows us to assert the presence and shape of mutable data structures on the heap, while the resource component allows us to state the consumable resources associated with each member of the structure. We present the logic on a small imperative language, based on Java bytecode, with procedures and mutable heap. We have formalised the logic and its soundness property within the Coq proof assistant and extracted a certified verification condition generator. We also describe an proof search procedure that allows generated verification conditions to be discharged while using linear programming to infer consumable resource annotations. We demonstrate the logic on some examples, including proving the termination of in-place list reversal on lists with cyclic tails.

Modeling the Java Bytecode Verifier

The Java programming language has been widely described as secure by design. Nevertheless, a number of serious security vulnerabilities have been discovered in Java, particularly in the Bytecode Verifier, a critical component used to verify class semantics before loading is complete. This paper describes a method for representing Java security constraints using the Alloy modeling language. It further describes a system for performing a security analysis on any block of Java bytecodes by converting these bytecodes into relation initializers in Alloy. Any counterexamples found by the Alloy analyzer correspond directly to potentially insecure code. Analysis of the approach is provided in the context of known security exploits, including type confusion attacks, invalid memory accesses and control flow misdirection. This type of analysis represents a significant departure from standard malware analysis methods based on signatures or anomaly detection.

Flight of the FINCH Through the Java Wilderness

We describe Fertile Darwinian Bytecode Harvester (FINCH), a methodology for evolving Java bytecode, enabling the evolution of extant, unrestricted Java programs, or programs in other languages that compile to Java bytecode. Our approach is based upon the notion of compatible crossover, which produces correct programs by performing operand stack-based, local variables-based, and control flow-based compatibility checks on source and destination bytecode sections. This is in contrast to existing work that uses restricted subsets of the Java bytecode instruction set as a representation language for individuals in genetic programming. We demonstrate FINCH's unqualified success at solving a host of problems, including simple and complex regression, trail navigation, image classification, array sum, and tic-tac-toe. FINCH exploits the richness of the Java virtual machine architecture and type system, ultimately evolving human-readable solutions in the form of Java programs. The ability to evolve Java programs will hopefully lead to a valuable new tool in the software engineer's toolkit.

A software tool for semi-automatic gridification of resource-intensive Java bytecodes and its application to ray tracing and sequence alignment

Computational Grids deliver the necessary computational infrastructure to perform resource-intensive computations such as the ones that solve the problems scientists are facing today. Exploiting Computational Grids comes at the expense of explicitly adapting the ordinary software implementing scientific problems to take advantage of Grid resources, which unavoidably requires knowledge on Grid programming. The recent notion of “gridifying” ordinary applications, which is based on semi-automatically deriving a Grid-aware version from the compiled code of a sequential application, promises users to be relieved from the requirement of manual usage of Grid APIs within their source codes. In this paper, we describe a novel gridification tool that allows users to easily parallelize Java applications on Grids. Extensive experiments with two real-world applications – ray tracing and sequence alignment – suggest that our approach provides a convenient balance between ease of gridification and Grid resource exploitation compared to manually using Grid APIs for gridifying ordinary applications.

A Dozen Instructions Make Java Bytecode

One of the biggest obstacles in the formalisation of the Java bytecode is that the language consists of 200 instructions. However, a rigorous handling of a programming language in the context of program verification and error detection requires a formalism which is compact in size. Therefore, the actual Java bytecode instruction set is never used in the context. Instead, the existing formalisations usually cover a ‘representative’ set of instructions. This paper describes how to reduce the number of instructions in a systematic and rigorous way into a manageable set of more general operations that cover the full functionality of the Java bytecode. The factorisation of the instruction set is based on the use of the runtime structures such as operand stack, heap etc. This is achieved by presentation of a formal semantics for the Java Virtual Machine.

Reconstruction of Type Information from Java Bytecode for Component Compatibility

The Java type system is strictly checked by both the compiler and the runtime bytecode interpreter of the JVM. These mechanisms together guarantee appropriate usage of class instances. Using modern component systems can however circumvent these static checks, because incompatible versions of classes can be bound together during component installation or update. Such problematic bindings result in ClassCastException or NoSuchMethodException runtime errors. In this paper we describe a representation of Java language types suitable for checking component compatibility. The presented approach applies various bytecode handling techniques to reconstruct a representation of the Java types contained in a component implementation, using different sources of class data. The representation is then used during build- and run-time type system verifications with the aim to prevent these kinds of errors. We have successfully applied this approach to prevent OSGi component incompatibilities.

Encoding the Java Virtual Machine's Instruction Set

New toolkits that parse, analyze, and transform Java Bytecode are frequently developed from scratch to obtain a representation suitable for a particular purpose. But, while the functionality implemented by these toolkits to read in class files and do basic control- and data-flow analyses is comparable, it is implemented over and over again. Differences manifest themselves mainly in minor technical issues. To avoid the repetitive development of similar functionality, we have developed an XML-based language for specifying bytecode-based instruction sets. Using this language, we have encoded the instruction set of the Java Virtual Machine such that it can directly be used, e.g., to generate the skeleton of bytecode-based tools. The XML format hereby specifies both the format of the instructions and their effect on the stack and the local registers upon execution. This enables developers of static analyses to generate generic control- and data-flow analyses, e.g., an analysis that transforms Java Bytecode into static single assignment form. To assess the usefulness of our approach, we have used the encoding of the Java Virtual Machine's instruction set to develop a framework for the analysis and transformation of Java class files. The evaluation shows that using the specification significantly reduces the development effort when compared to manual development.

Exploring Online Synthesis for CGRAs with Specialized Operator Sets

The design of energy-efficient systems has become a major challenge for engineers over the last decade. One way to save energy is to spread out computations in space rather than in time (as traditional processors do). Unfortunately, this requires to design specialized hardware for each application. Also, the nonrecurring expenses for the manufacturing of chips continuously grow. Implementing the computations on FPGAs and CGRAs solves this dilemma, as the non recurring expenses are shared between many different applications. We believe that online synthesis that takes place during the execution of an application is one way to broaden the applicability of reconfigurable architectures as no expert knowledge of synthesis and technologies is required. In this paper, we give a detailed analysis of the amount and specialization of resources in a CGRA that are required to grant a significant speedup of Java bytecode. In fact, we show that even a relatively small number of specialized reconfigurable resources is sufficient to speed up applications considerably. Particularly, we look at the number of dedicated multipliers and dividers. Also, we discuss the required number of concurrent memory access operations inside the CGRA. Again, it shows that two concurrent memory access operations are sufficient for almost all applications.

Data obfuscation with network coding

Network coding techniques such as fountain codes are a promising way to disseminate large bulks of data in a multicast manner over an unreliable medium. In this work we investigate how to conceal such an encoded data stream on its way to numerous receivers with a minimum investment. Compared to conventional ‘encrypt – encode/decode – decrypt’ approaches, our solution is preferable for two reasons: First, it causes less CPU investment for encryption and decryption proportional to the ratio of the payload length to the signaling data length. Second, besides obfuscating the payload data from an eavesdropper, we hide the coding information from an eavesdropper. We evaluate the approach with respect to its application to various data types like MPEG-2 video streams and Java bytecode.

Formalisation and implementation of an algorithm for bytecode verification of @NonNull types

Java’s annotation mechanism allows us to extend its type system with non-null types. Checking such types cannot be done using the existing bytecode verification algorithm. We extend this algorithm to verify non-null types using a novel technique that identifies aliasing relationships between local variables and stack locations in the JVM. We formalise this for a subset of Java Bytecode and report on experiences using our implementation.

A pointcut-based coverage analysis approach for aspect-oriented programs

Aspect-oriented programming (AOP) is a promising technology that supports separation of crosscutting concerns ( i.e., functionality that tends to be tangled with, and scattered through the rest of the system). In AOP, a method-like construct named advice is applied to join points in the system through a special construct named pointcut. This mechanism supports the modularization of crosscutting behavior; however, since the added interactions are not explicit in the source code, it is hard to ensure their correctness. To tackle this problem, this paper presents a rigorous coverage analysis approach to ensure exercising the logic of each advice – statements, branches, and def-use pairs – at each affected join point. To make this analysis possible, a structural model based on Java bytecode – called PointCut-based Def-Use Graph ( PCDU ) – is proposed, along with three integration testing criteria. Theoretical, empirical, and exploratory studies involving 12 aspect-oriented programs and several fault examples present evidence of the feasibility and effectiveness of the proposed approach.

Parametric inference of memory requirements for garbage collected languages

The accurate prediction of program's memory requirements is a critical component in software development. Existing heap space analyses either do not take deallocation into account or adopt specific models of garbage collectors which do not necessarily correspond to the actual memory usage. We present a novel approach to inferring upper bounds on memory requirements of Java-like programs which is parametric on the notion of object lifetime , i.e., on when objects become collectible. If objects lifetimes are inferred by a reachability analysis, then our analysis infers accurate upper bounds on the memory consumption for a reachability -based garbage collector. Interestingly, if objects lifetimes are inferred by a heap liveness analysis, then we approximate the program minimal memory requirement, i.e., the peak memory usage when using an optimal garbage collector which frees objects as soon as they become dead. The key idea is to integrate information on objects lifetimes into the process of generating the recurrence equations which capture the memory usage at the different program states. If the heap size limit is set to the memory requirement inferred by our analysis, it is ensured that execution will not exceed the memory limit with the only assumption that garbage collection works when the limit is reached. Experiments on Java bytecode programs provide evidence of the feasibility and accuracy of our analysis.

Comprehensive aspect weaving for Java

Aspect-oriented programming (AOP) has been successfully applied to application code thanks to techniques such as Java bytecode instrumentation. Unfortunately, with existing AOP frameworks for Java such as AspectJ, aspects cannot be woven into the standard Java class library. This restriction is particularly unfortunate for aspects that would benefit from comprehensive aspect weaving with complete method coverage, such as profiling or debugging aspects. In this article we present MAJOR, a new tool for comprehensive aspect weaving, which ensures that aspects are woven into all classes loaded in a Java Virtual Machine, including those in the standard Java class library. MAJOR includes the pluggable module CARAJillo, which supports efficient access to a complete and customizable calling context representation. We validate our approach with three case studies. Firstly, we weave existing profiling aspects with MAJOR which otherwise would generate incomplete profiles. Secondly, we introduce an aspect for memory leak detection that also benefits from comprehensive weaving. Thirdly, we present an aspect subsuming the functionality of ReCrash, an existing tool based on low-level bytecode instrumentation techniques that generates unit tests to reproduce program failures. Our aspect-based tools are concisely implemented in a few lines of code, and leverage MAJOR and CARAJillo for comprehensive aspect weaving and for efficient access to calling context information.

Worst‐case execution time analysis for a Java processor

AbstractIn this paper, we propose a solution for a worst‐case execution time (WCET) analyzable Java system: a combination of a time‐predictable Java processor and a tool that performs WCET analysis at Java bytecode level. We present a Java processor, called JOP, designed for time‐predictable execution of real‐time tasks. The execution time of bytecodes, the instructions of the Java virtual machine, is known to cycle accuracy for JOP. Therefore, JOP simplifies the low‐level WCET analysis. A method cache, which fills whole Java methods into the cache, simplifies cache analysis. The WCET analysis tool is based on integer linear programming. The tool performs the low‐level analysis at the bytecode level and integrates the method cache analysis. An integrated data‐flow analysis performs receiver‐type analysis for dynamic method dispatches and loop‐bound analysis. Furthermore, a model checking approach to WCET analysis is presented where the method cache can be exactly simulated. The combination of the time‐predictable Java processor and the WCET analysis tool is evaluated with standard WCET benchmarks and three real‐time applications. The WCET friendly architecture of JOP and the integrated method cache analysis yield tight WCET bounds. Comparing the exact, but expensive, model checking‐based analysis of the method cache with the static approach demonstrates that the static approximation of the method cache is sufficiently tight for practical purposes. Copyright © 2010 John Wiley & Sons, Ltd.

Verifying Temporal Regular Properties of Abstractions of Term Rewriting Systems

The tree automaton completion is an algorithm used for proving safety properties of systems that can be modeled by a term rewriting system. This representation and verification technique works well for proving properties of infinite systems like cryptographic protocols or more recently on Java Bytecode programs. This algorithm computes a tree automaton which represents a (regular) over approximation of the set of reachable terms by rewriting initial terms. This approach is limited by the lack of information about rewriting relation between terms. Actually, terms in relation by rewriting are in the same equivalence class: there are recognized by the same state in the tree automaton. Our objective is to produce an automaton embedding an abstraction of the rewriting relation sufficient to prove temporal properties of the term rewriting system. We propose to extend the algorithm to produce an automaton having more equivalence classes to distinguish a term or a subterm from its successors w.r.t. rewriting. While ground transitions are used to recognize equivalence classes of terms, epsilon-transitions represent the rewriting relation between terms. From the completed automaton, it is possible to automatically build a Kripke structure abstracting the rewriting sequence. States of the Kripke structure are states of the tree automaton and the transition relation is given by the set of epsilon-transitions. States of the Kripke structure are labelled by the set of terms recognized using ground transitions. On this Kripke structure, we define the Regular Linear Temporal Logic (R-LTL) for expressing properties. Such properties can then be checked using standard model checking algorithms. The only difference between LTL and R-LTL is that predicates are replaced by regular sets of acceptable terms.

Magic-sets for localised analysis of Java bytecode

Static analyses based on denotational semantics can naturally model functional behaviours of the code in a compositional and completely context and flow sensitive way. But they only model the functional i.e., input/output behaviour of a program P, not enough if one needs P’s internal behaviours i.e., from the input to some internal program points. This is, however, a frequent requirement for a useful static analysis. In this paper, we overcome this limitation, for the case of mono-threaded Java bytecode, with a technique used up to now for logic programs only. Namely, we define a program transformation that adds new magic blocks of code to the program P, whose functional behaviours are the internal behaviours of P. We prove the transformation correct w.r.t. an operational semantics and define an equivalent denotational semantics, devised for abstract interpretation, whose denotations for the magic blocks are hence the internal behaviours of P. We implement our transformation and instantiate it with abstract domains modelling sharing of two variables, non-cyclicity of variables, nullness of variables, class initialisation information and size of the values bound to program variables. We get a static analyser for full mono-threaded Java bytecode that is faster and scales better than another operational pair-sharing analyser. It has the same speed but is more precise than a constraint-based nullness analyser. It makes a polyhedral size analysis of Java bytecode scale up to 1300 methods in a couple of minutes and a zone-based size analysis scale to still larger applications.

A termination analyzer for Java bytecode based on path-length

It is important to prove that supposedly terminating programs actually terminate, particularly if those programs must be run on critical systems or downloaded into a client such as a mobile phone. Although termination of computer programs is generally undecidable, it is possible and useful to prove termination of a large, nontrivial subset of the terminating programs. In this article, we present our termination analyzer for sequential Java bytecode, based on a program property called path-length . We describe the analyses which are needed before the path-length can be computed such as sharing, cyclicity, and aliasing. Then we formally define the path-length analysis and prove it correct with respect to a reference denotational semantics of the bytecode. We show that a constraint logic program P CLP can be built from the result of the path-length analysis of a Java bytecode program P and formally prove that if P CLP terminates, then P also terminates. Hence a termination prover for constraint logic programs can be applied to prove the termination of P . We conclude with some discussion of the possibilities and limitations of our approach. Ours is the first existing termination analyzer for Java bytecode dealing with any kind of data structures dynamically allocated on the heap and which does not require any help or annotation on the part of the user.

Toward robustly protecting data of a dominant path in a java method

This paper presents an approach to robustly protect the data of a dominant path in a method of a Java bytecode program by integrating oblivious hashing, guards network, and control flow obfuscation. A dominator tree based on the basic blocks of the target method is first built. Then the dominant path of the dominator tree is selected. The bytecodes of the dominant path are then transformed by the oblivious hashing, guards network, and control flow obfuscation. Oblivious hashing is not directly applicable for bytecodes. We extend the oblivious hashing for Java to monitor the stack. The guards network makes copies of the hash values generated by oblivious hashing, hides the copies in the method and inserts codes for checking the values of these copies in different basic blocks. Finally, the method is transformed by one of the three control flow obfuscations at random, which not only increases the complexity of the guards network but also prevents decompilation of the program. A bytecode simulator is developed to evaluate and compromise the incidents of adding the protective bytecodes and to make the protected program pass the JVM verifier. We used CaffeineMark 3.0 as the benchmark. The measured performance degradation was from 1.2% to 61.3%.