Peter Ohmann

Assistant Professor of Computer Science at
Xavier University

Projects

csi-cc

An instrumenting compiler for lightweight, customizable tracing of deployed C/C++ applications.

csi-grissom

An analysis framework for answering user control-flow queries over incomplete failure reports.

CSIclipse

A plugin for presenting CSI instrumentation and analysis data in the Eclipse IDE.

Publications

Full publication list

Please see my Google Scholar page.

Selected/Upcoming conference preprints

Debugging is difficult. When software fails in production, debugging is even harder, as failure reports usually provide only an incomplete picture of the failing execution. We present a system that answers control-flow queries posed by developers as formal languages, indicating whether the query expresses control flow that is possible or impossible for a given failure report. We consider three separate approaches that trade off precision, expressiveness for failure constraints, and scalability. We also introduce a new subclass of regular languages, the unreliable trace languages, which are particularly suited to answering control-flow queries in polynomial time. Our system answers queries remarkably efficiently when we encode failure constraints and user queries entirely as unreliable trace languages.

See also our accompanying technical report.

Program coverage is used across many stages of software development. While common during testing, program coverage has also found use outside the test lab, in production software. However, production software has stricter requirements on run-time overheads, and may limit possible program instrumentation. Thus, optimizing the placement of probes to gather program coverage is important.

We introduce and study the problem of customized program coverage optimization. We generalize previous work that optimizes for complete coverage instrumentation with a system that adapts optimization to customizable program coverage requirements. Specifically, our system allows a user to specify desired coverage locations and to limit legal instrumentation locations. We prove that the problem of determining optimal coverage probes is NP-hard, and we present a solution based on mixed integer linear programming. Due to the computational complexity of the problem, we also provide two practical approximation approaches. We evaluate the effectiveness of our approximations across a diverse set of benchmarks, and show that our techniques can substantially reduce instrumentation while allowing the user immense freedom in defining coverage requirements. When naïve instrumentation is dense or expensive, our optimizations succeed in lowering execution time overheads.

See also our accompanying technical report.

This is an extended journal version of our ASE 2013 paper which was awarded an ACM SIGSOFT Distinguished Paper Award.

Debugging is difficult and costly. As a human programmer looks for a bug, it would be helpful to see a complete trace of events leading to the point of failure. Unfortunately, full tracing is simply too slow to use after deployment, and may even be impractical during testing.

We aid post-deployment debugging by giving programmers additional information about program activity shortly before failure. We use latent information in post-failure memory dumps, augmented by low-overhead, tunable run-time tracing. Our results with a realistically-tuned tracing scheme show low enough overhead (0–5%) to be used in production runs. We demonstrate several potential uses of this enhanced information, including a novel postmortem static slice restriction technique and a reduced view of potentially-executed code. Experimental evaluation shows our approach to be very effective. For example, our analyses shrink interprocedural static slices by 53–78% in larger applications.

Debugging is difficult and costly, especially for failures that occur after deployment. In prior work, we developed a suite of instrumentation and analysis tools, collectively titled the Crash Scene Investigation toolkit (CSI). These tools aid developers by providing additional information about failing program executions using latent data in post-failure memory dumps. While we showed that our technique is effective in reducing execution ambiguity, it lacked a proper user interface for developers.

In this paper, we present CSIclipse, a work-in-progress plugin for the Eclipse integrated development environment (IDE) that brings our analyses directly to the user. The goal of our plugin is to ease the burden of debugging production failures by conveniently presenting CSI trace and analysis data with intuitive source code overlays and powerful data exploration mechanisms. While designed for our CSI data, our plugin is likely general enough to support trace data from a variety of program analyses.

Philosophy

I have also done some research in philosophy, primarily focused on the Modern period. I have posted a draft of the first few sections of an in-progress paper on the issue of numerical identify in Immanuel Kant's critical philosophy. You can find the draft here.