The Use of Program Profiling for Software Maintenance
with Applications to the Year 2000 Problem
Thomas Reps, Thomas Ball, Manuvir Das, and James Larus
This paper describes new techniques to help with testing and
debugging, using information obtained from path profiling. A path
profiler instruments a program so that the number of times each
different loop-free path executes is accumulated during an execution
run. With such an instrumented program, each run of the program
generates a path spectrum for the execution --- a distribution of the
paths that were executed during that run. A path spectrum is a
finite, easily obtainable characterization of a program's execution on
a dataset, and provides a behavior signature for a run of the program.
Our techniques are based on the idea of comparing path spectra from
different runs of the program. When different runs produce different
spectra, the spectral differences can be used to identify paths in the
program along which control diverges in the two runs. By choosing
input datasets to hold all factors constant except one, the divergence
can be attributed to this factor. The point of divergence itself may
not be the cause of the underlying problem, but provides a starting
place for a programmer to begin his exploration.
One application of this technique is in the "Year 2000 Problem" (i.e.,
the problem of fixing computer systems that use only 2-digit year
fields in date-valued data). In this context, path-spectrum
comparison provides a heuristic for identifying paths in a program
that are good candidates for being date-dependent computations. The
application of path-spectrum comparison to a number of other
software-maintenance issues is also discussed.
Key Words and Phrases:
Path profiling, path-spectrum comparison, testing, debugging, year
2000 problem, date-dependent computations, self-monitoring programs.
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