4,475 research outputs found
Lightweight Support for Magic Wands in an Automatic Verifier (Artifact)
This artifact is based on Silicon, which is an automatic verification tool for programs written in the Silver Intermediate Verification Language. Silver is designed to natively support permission-based reasoning, in the style of separation logic and similar approaches. Our extension of Silicon provides support for specification and verification of programs using the magic wand operator, which can be used to represent ways to exchange views on the program state, or to represent partial versions of data structures. Our implementation is a backwards-compatible extension of the basic tool, and is provided along with a test suite of examples and regressions in a VirtualBox image. Instructions for running our tool on these (and user-defined) examples are provided in the image, to allow users to experiment with the verifier
Local Reasoning for Global Graph Properties
Separation logics are widely used for verifying programs that manipulate
complex heap-based data structures. These logics build on so-called separation
algebras, which allow expressing properties of heap regions such that
modifications to a region do not invalidate properties stated about the
remainder of the heap. This concept is key to enabling modular reasoning and
also extends to concurrency. While heaps are naturally related to mathematical
graphs, many ubiquitous graph properties are non-local in character, such as
reachability between nodes, path lengths, acyclicity and other structural
invariants, as well as data invariants which combine with these notions.
Reasoning modularly about such graph properties remains notoriously difficult,
since a local modification can have side-effects on a global property that
cannot be easily confined to a small region.
In this paper, we address the question: What separation algebra can be used
to avoid proof arguments reverting back to tedious global reasoning in such
cases? To this end, we consider a general class of global graph properties
expressed as fixpoints of algebraic equations over graphs. We present
mathematical foundations for reasoning about this class of properties, imposing
minimal requirements on the underlying theory that allow us to define a
suitable separation algebra. Building on this theory we develop a general proof
technique for modular reasoning about global graph properties over program
heaps, in a way which can be integrated with existing separation logics. To
demonstrate our approach, we present local proofs for two challenging examples:
a priority inheritance protocol and the non-blocking concurrent Harris list
A unified framework for verification techniques for object invariants
Object invariants define the consistency of objects. They have subtle semantics, mainly because of call-backs, multi-object invariants, and subclassing. Several verification techniques for object invariants have been proposed. It is difficult to compare these techniques, and to ascertain their soundness, because of their differences in restrictions on programs and invariants, in the use of advanced type systems (e.g., ownership types), in the meaning of invariants, and in proof obligations. We develop a unified framework for such techniques. We distil seven parameters that characterise a verification technique, and identify sufficient conditions on these parameters which guarantee soundness. We instantiate our framework with three verification techniques from the literature, and use it to assess soundness and compare expressiveness.peer-reviewe
Automating Deductive Verification for Weak-Memory Programs
Writing correct programs for weak memory models such as the C11 memory model
is challenging because of the weak consistency guarantees these models provide.
The first program logics for the verification of such programs have recently
been proposed, but their usage has been limited thus far to manual proofs.
Automating proofs in these logics via first-order solvers is non-trivial, due
to reasoning features such as higher-order assertions, modalities and rich
permission resources. In this paper, we provide the first implementation of a
weak memory program logic using existing deductive verification tools. We
tackle three recent program logics: Relaxed Separation Logic and two forms of
Fenced Separation Logic, and show how these can be encoded using the Viper
verification infrastructure. In doing so, we illustrate several novel encoding
techniques which could be employed for other logics. Our work is implemented,
and has been evaluated on examples from existing papers as well as the Facebook
open-source Folly library.Comment: Extended version of TACAS 2018 publicatio
The Diagnostic Potential of Transition Region Lines under-going Transient Ionization in Dynamic Events
We discuss the diagnostic potential of high cadence ultraviolet spectral data
when transient ionization is considered. For this we use high cadence UV
spectra taken during the impulsive phase of a solar flares (observed with
instruments on-board the Solar Maximum Mission) which showed excellent
correspondence with hard X-ray pulses. The ionization fraction of the
transition region ion O V and in particular the contribution function for the O
V 1371A line are computed within the Atomic Data and Analysis Structure, which
is a collection of fundamental and derived atomic data and codes which
manipulate them. Due to transient ionization, the O V 1371A line is enhanced in
the first fraction of a second with the peak in the line contribution function
occurring initially at a higher electron temperature than in ionization
equilibrium. The rise time and enhancement factor depend mostly on the electron
density. The fractional increase in the O V 1371A emissivity due to transient
ionization can reach a factor of 2--4 and can explain the fast response in the
line flux of transition regions ions during the impulsive phase of flares
solely as a result of transient ionization. This technique can be used to
diagnostic the electron temperature and density of solar flares observed with
the forth-coming Interface Region Imaging Spectrograph.Comment: 18 pages, 6 figure
Microlocal analysis of quantum fields on curved spacetimes: Analytic wavefront sets and Reeh-Schlieder theorems
We show in this article that the Reeh-Schlieder property holds for states of
quantum fields on real analytic spacetimes if they satisfy an analytic
microlocal spectrum condition. This result holds in the setting of general
quantum field theory, i.e. without assuming the quantum field to obey a
specific equation of motion. Moreover, quasifree states of the Klein-Gordon
field are further investigated in this work and the (analytic) microlocal
spectrum condition is shown to be equivalent to simpler conditions. We also
prove that any quasifree ground- or KMS-state of the Klein-Gordon field on a
stationary real analytic spacetime fulfills the analytic microlocal spectrum
condition.Comment: 31 pages, latex2
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