Improving WCET Analysis Precision through Automata Product

Real-time scheduling of application requires sound estimation of the Worst-Case Execution Time (WCET) of each task. Part of the over-approximation introduced by the WCET analysis of a task comes from not taking into account the fact that the (implicit) worst-case execution path may be infeasible. This article does not address the question of finding infeasible paths but provides a new formalism of automata to describe sets of infeasible paths. This formalism combines the possibilities to express state-based path acceptance (like in regular automata), constraints on counters (in the Implicit Path Enumeration Technique fashion) and contexts of validity (like in State charts). We show the applicability of our proposal by performing infeasible paths aware WCET analyses within the OTAWA framework. We provide algorithms that transform the control flow graph and/or the constraints system supporting the WCET analysis in order to exclude the specified paths

Quantitative Static Analysis Over Semirings: Analysing Cache Behaviour for Java Card

AbstractWe present a semantics-based technique for modeling and analysing resource usage behaviour of programs written in a simple object oriented language like Java Card byte code. The approach is based on the quantitative abstract interpretation framework of Di Pierro and Wiklicky where programs are represented as linear operators. We consider in particular linear operators over semi-rings (such as max-plus) that have proven useful for analysing cost properties of discrete event systems. We illustrate our technique through a cache behaviour analysis for Java Card

Hierarchical Shape Abstraction of Dynamic Structures in Static Blocks

International audienceWe propose a hierarchical shape abstract domain, so as to infer structural invariants of dynamic structures such as lists living inside static structures, such as arrays. This programming pattern is often used in safety critical embedded software that need to ''allocate'' dynamic structures inside static regions due to dynamic memory allocation being forbidden in this context. Our abstract domain precisely describes such hierarchies of structures. It combines several instances of simple shape abstract domains, dedicated to the representation of elementary shape properties, and also embeds a numerical abstract domain. This modular construction greatly simplifies the design and the implementation of the abstract domain. We provide an implementation, and show the effectiveness of our approach on a problem taken from a real code

Quantitative Static Analysis over semirings: analysing cache behaviour for Java Card

Abstract We present a semantics-based technique for modeling and analysing resource usage behaviour of programs written in a simple object oriented language like Java Card byte code. The approach is based on the quantitative abstract interpretation framework of Di Pierro and Wiklicky where programs are represented as linear operators. We consider in particular linear operators over semi-rings (such as max-plus) that have proven useful for analysing cost properties of discrete event systems. We illustrate our technique through a cache behaviour analysis for Java Card

From Relevant High-level Properties to WCET Computation Improvement

The scheduling of real-time systems requires knowing the Worst Case Execution Time (WCET) of their tasks. WCET analysers compute timings by analysis of the low level behaviour of the target task. This document presents improvements in the WCET computation allowed by taking into account high level behaviours of the tasks. We first classify high level knowledge according to the relevance with respect to WCET estimation. We then propose a systematic method to bring this information back to the low level on which operate most WCET analysers. This approach separates the concerns of stating properties, integrating properties and computing a WCET aware of these properties

When the worst-case execution time estimation gains from the application semantics

International audienceCritical embedded systems are generally composed of repetitive tasks that must meet drastic timing constraints, such as termination deadlines. Providing an upper bound of the worst-case execution time (WCET) of such tasks at design time is thus necessary to prove the correctness of the system. Static timing analysis methods compute safe WCET upper bounds, but at the cost of a potentially large over-approximation. Over-approximation may come from the fact that WCET analysis may consider as potential worst-cases some executions that are actually infeasible, because of the semantics of the program and/or because they correspond to unrealistic inputs. In this paper, we introduce a complete semantic-aware WCET estimation workflow. We introduce some program analysis to find infeasible paths: they can be performed at design, C or binary level, and may take into account information provided by the user. We design an annotation-aware compilation process that enables to trace the infeasible path properties through the program transformations performed by the compilers. Finally, we adapt the WCET estimation tool to take into account the kind of annotations produced by the workflow

Transient conditions for biogenesis on low-mass exoplanets with escaping hydrogen atmospheres

Exoplanets with lower equilibrium temperatures than Earth and primordial hydrogen atmospheres that evaporate after formation should pass through transient periods where oceans can form on their surfaces, as liquid water can form below a few thousand bar pressure and H2-H2 collision-induced absorption provides significant greenhouse warming. The duration of the transient period depends on the planet size, starting H2 inventory and star type, with the longest periods typically occurring for planets around M-class stars. As pre-biotic compounds readily form in the reducing chemistry of hydrogen-rich atmospheres, conditions on these planets could be favourable to the emergence of life. The ultimate fate of any emergent organisms under such conditions would depend on their ability to adapt to (or modify) their gradually cooling environment.Comment: 19 pages, 5 figures, accepted for publication in Icaru

LAPLACE: A mission to Europa and the Jupiter System for ESA's Cosmic Vision Programme

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