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WALA

Simple Story

The T. J. Watson Libraries for Analysis (WALA) build the full map of which method can call which, then ask whether any route leads from the pupil's desk to something forbidden.

Where the simpler engine asks "does this class mention that one?", WALA asks "can I get there from here, however many steps it takes?"

What it is​

WALA (T. J. Watson Libraries for Analysis) is a static analysis framework from IBM Research. It builds inter-procedural call graphs and supports data-flow analysis over them.

How Ares 2 uses it​

WALA is the second architecture engine, selected by the WALA half of the programming language configuration. It builds a call graph from the entry point named in theMainClassInsideThisPackageIs and searches for paths from student code to forbidden sinks.

This finds indirect access that dependency analysis misses: a student method that calls a helper that calls a library method that opens a file has no direct dependency on the file application programming interface (API), but there is a path.

WalaPathClassification decides which parts of a discovered path are student code and which are trusted infrastructure. Its RESERVED_PACKAGE_PREFIX_VERSION is the versioned prefix list that the build-side reserved-package boundary must stay aligned with.

The cost​

Whole-program call-graph construction is far more expensive than dependency analysis, and reachability over an over-approximated graph produces false positives that have to be filtered. That trade is the reason both engines exist rather than one.

Further reading​