[Pl-seminar] 10/13 Seminar: Thomas Wahl, Behavioral Non-Portability in Decision-Making Programs

[Daniel Patterson]

NUPRL Seminar presents

Thomas Wahl
Northeastern University

12:00pm-1:30pm
Thursday, Oct. 13 2016
Room 366 WVH (http://www.ccs.neu.edu/home/wand/directions.html)


Behavioral Non-Portability in Decision-Making Programs

Abstract:

The precise semantics of floating-point arithmetic programs depends on the
execution platform, including the compiler and the target hardware. Such
platform dependencies infringe on the highly desirable goal of software
portability (which is in fact promised by heterogeneous computing
frameworks like OpenCL): the same program run on the same inputs on
different platforms can produce different results. In other words,
portability does not guarantee reproducibility, and this is a more or less
accepted state of affairs.

Serious doubts on the portability of numeric applications arise when
differences in results are behavioral, i.e. when they lead to changes in
the control flow of a program. In this talk I will first present an
algorithm that takes a numeric procedure and determines whether a given
input can lead to different decisions depending merely on how the
arithmetic in the procedure is compiled and executed. I will then show how
this algorithm can be used in static and dynamic analyses of programs, to
estimate their numeric stability. I will illustrate the results on examples
characteristic of numeric computing where control flow divergence actually
occurs across different execution platforms.

Joint with Yijia Gu, Mahsa Bayati, and Miriam Leeser, Northeastern
University, Boston, USA

Bio:
Thomas Wahl joined the faculty of Northeastern University in 2011. His
research concerns the reliability (whatever that means) of complex
computing systems. Two domains notorious for their fragility are
concurrency and numerical computing. With colleagues, Wahl has investigated
how floating-point arithmetic can "hijack" a program's computation when run
on non-standard architectures, such as heterogeneous and custom-made
embedded platforms. You will witness some hijacking attempts in the talk
today.
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