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Carrying Code (ACC) has recently been proposed as a framework for mobile code safety in which the code supplier provides a program together with an abstraction (or abstract model of the program) whose validity entails compliance with a predefined safety policy. The advantage of providing a (fixpoint) abstraction to the code consumer is that its validity is checked in a single pass (i.e., one iteration) of an abstract interpretation-based checker. A main challenge to make ACC useful in practice is to reduce the size of certificates as much as possible while at the same time not increasing checking time. The intuitive idea is to only include in the certificate information that the checker is unable to reproduce without iterating. We introduce the notion of reduced certificate which characterizes the subset of the abstraction which a checker needs in order to validate (and re-construct) the full certificate in a single pass. Based on this notion, we instrument a generic analysis algorithm with the necessary extensions in order to identify the information relevant to the checker. Interestingly, the fact that the reduced certificate omits (parts of) the abstraction has implications in the design of the checker. We provide the sufficient conditions which allow us to ensure that 1) if the checker succeeds in validating the certificate, then the certificate is valid for the program (correctness) and 2) the checker will succeed for any reduced certificate which is valid (completeness). Our approach has been implemented and benchmarked within the ciaopp system. The experimental results show that our proposal is able to greatly reduce the size of certificates in practice.To appear in Theory and Practice of Logic Programming (TPLP)., Comment: 35 pages, 1 figure, 2 tables

Testing is a vital part of the software development process. Test Case Generation (TCG) is the process of automatically generating a collection of test cases which are applied to a system under test. White-box TCG is usually performed by means of symbolic execution, i.e., instead of executing the program on normal values (e.g., numbers), the program is executed on symbolic values representing arbitrary values. When dealing with an object-oriented (OO) imperative language, symbolic execution becomes challenging as, among other things, it must be able to backtrack, complex heap-allocated data structures should be created during the TCG process and features like inheritance, virtual invocations and exceptions have to be taken into account. Due to its inherent symbolic execution mechanism, we pursue in this paper that Constraint Logic Programming (CLP) has a promising unexploited application field in TCG. We will support our claim by developing a fully CLP-based framework to TCG of an OO imperative language, and by assessing it on a corresponding implementation on a set of challenging Java programs. A unique characteristic of our approach is that it handles all language features using only CLP and without the need of developing specific constraint operators (e.g., to model the heap).

State of the art analyzers in the Logic Programming (LP) paradigm are nowadays mature and sophisticated. They allow inferring a wide variety of global properties including termination, bounds on resource consumption, etc. The aim of this work is to automatically transfer the power of such analysis tools for LP to the analysis and verification of Java bytecode (JVML). In order to achieve our goal, we rely on well-known techniques for meta-programming and program specialization. More precisely, we propose to partially evaluate a JVML interpreter implemented in LP together with (an LP representation of) a JVML program and then analyze the residual program. Interestingly, at least for the examples we have studied, our approach produces very simple LP representations of the original JVML programs. This can be seen as a decompilation from JVML to high-level LP source. By reasoning about such residual programs, we can automatically prove in the CiaoPP system some non-trivial properties of JVML programs such as termination, run-time error freeness and infer bounds on its resource consumption. We are not aware of any other system which is able to verify such advanced properties of Java bytecode.

In recent work, we have proposed an approach to Test Data Generation (TDG) of imperative bytecode by partial evaluation (PE) of CLP which consists in two phases: (1) the bytecode program is first transformed into an equivalent CLP program by means of interpretive compilation by PE, (2) a second PE is performed in order to supervise the generation of test-cases by execution of the CLP decompiled program. The main advantages of TDG by PE include flexibility to handle new coverage criteria, the possibility to obtain test-case generators and its simplicity to be implemented. The approach in principle can be directly applied for TDG of any imperative language. However, when one tries to apply it to a declarative language like Prolog, we have found as a main difficulty the generation of test-cases which cover the more complex control flow of Prolog. Essentially, the problem is that an intrinsic feature of PE is that it only computes non-failing derivations while in TDG for Prolog it is essential to generate test-cases associated to failing computations. Basically, we propose to transform the original Prolog program into an equivalent Prolog program with explicit failure by partially evaluating a Prolog interpreter which captures failing derivations w.r.t. the input program. Another issue that we discuss in the paper is that, while in the case of bytecode the underlying constraint domain only manipulates integers, in Prolog it should properly handle the symbolic data manipulated by the program. The resulting scheme is of interest for bringing the advantages which are inherent in TDG by PE to the field of logic programming., Comment: Paper presented at the 18th Workshop on Logic-based Methods in Programming Environments (WLPE2008) (Report-No: WLPE/2008). Paper submitted by a co-editor of the Workshop proceedings

Abstraction-Carrying Code (ACC) has recently been proposed as a framework for proof-carrying code (PCC) in which the code supplier provides a program together with an abstraction (or abstract model of the program) whose validity entails compliance with a predefined safety policy. The abstraction thus plays the role of safety certificate and its generation (and validation) is carried out automatically by a fixed-point analyzer. Existing approaches for PCC are developed under the assumption that the consumer reads and validates the entire program w.r.t. the full certificate at once, in a non incremental way. In this abstract, we overview the main issues on incremental ACC. In particular, in the context of logic programming, we discuss both the generation of incremental certificates and the design of an incremental checking algorithm for untrusted updates of a (trusted) program, i.e., when a producer provides a modified version of a previously validated program. By update, we refer to any arbitrary change on a program, i.e., the extension of the program with new predicates, the deletion of existing predicates and the replacement of existing predicates by new versions for them. We also discuss how each kind of update affects the incremental extension in terms of accuracy and correctness., Comment: Paper presented at the 16th Workshop on Logic-based Methods in Programming Environments (WLPE2006)

Effective static analyses have been proposed which infer bounds on the number of resolutions or reductions. These have the advantage of being independent from the platform on which the programs are executed and have been shown to be useful in a number of applications, such as granularity control in parallel execution. On the other hand, in distributed computation scenarios where platforms with different capabilities come into play, it is necessary to express costs in metrics that include the characteristics of the platform. In particular, it is specially interesting to be able to infer upper and lower bounds on actual execution times. With this objective in mind, we propose an approach which combines compile-time analysis for cost bounds with a one-time profiling of the platform in order to determine the values of certain parameters for a given platform. These parameters calibrate a cost model which, from then on, is able to compute statically time bound functions for procedures and to predict with a significant degree of accuracy the execution times of such procedures in the given platform. The approach has been implemented and integrated in the CiaoPP system., Comment: Paper presented at the 16th Workshop on Logic-based Methods in Programming Environments

The relationship between abstract interpretation and partial deduction has received considerable attention and (partial) integrations have been proposed starting from both the partial deduction and abstract interpretation perspectives. In this work we present what we argue is the first fully described generic algorithm for efficient and precise integration of abstract interpretation and partial deduction. Taking as starting point state-of-the-art algorithms for context-sensitive, polyvariant abstract interpretation and (abstract) partial deduction, we present an algorithm which combines the best of both worlds. Key ingredients include the accurate success propagation inherent to abstract interpretation and the powerful program transformations achievable by partial deduction. In our algorithm, the calls which appear in the analysis graph are not analyzed w.r.t. the original definition of the procedure but w.r.t. specialized definitions of these procedures. Such specialized definitions are obtained by applying both unfolding and abstract executability. Our framework is parametric w.r.t. different control strategies and abstract domains. Different combinations of such parameters correspond to existing algorithms for program analysis and specialization. Simultaneously, our approach opens the door to the efficient computation of strictly more precise results than those achievable by each of the individual techniques. The algorithm is now one of the key components of the CiaoPP analysis and specialization system., Comment: In A. Serebrenik and S. Munoz-Hernandez (editors), Proceedings of the 15th Workshop on Logic-based methods in Programming Environments October 2005, Sitges. cs.PL/0508078