Timestamped whole program path representation and its applications

Abstract

A whole program path (WPP) is a complete control flow trace of a program's execution. Recently Larus [18] showed that although WPP is expected to be very large (100's of MBytes), it can be greatly compressed (to 10's of MBytes) and therefore saved for future analysis. While the compression algorithm proposed by Larus is highly effective, the compression is accompanied with a loss in the ease with which subsets of information can be accessed. In particular, path traces pertaining to a particular function cannot generally be obtained without examining the entire compressed WPP representation. To solve this problem we advocate the application of compaction techniques aimed at providing easy access to path traces on a per function basis. We present a WPP compaction algorithm in which the WPP is broken in to path traces corresponding to individual function calls. All of the path traces for a given function are stored together as a block. Ability to construct the complete WPP from individual path traces is preserved by maintaining a dynamic call graph . The compaction is achieved by eliminating redundant path traces that result from different calls to a function and by replacing a sequence of static basic block ids that correspond to a dynamic basic block by a single id. We transform a compacted WPP representation into a timestamped WPP (TWPP) representation in which the path traces are organized from the perspective of dynamic basic blocks. TWPP representation also offers additional opportunities for compaction. Experiments show that our algorithm compacts the WPPs by factors ranging from 7 to 64. At the same time information is organized in a highly accessible form which speeds up the responses to queries requesting the path traces of a given function by over 3 orders of magnitude.

Unified control flow and data dependence traces

“…There are two kinds of explicit representations: those that are more appropriate to use when the traces are stored on disk, such as the Sequitur [Nevil-Manning and Witten 1997] compressed control flow trace representation called the whole-program path [Larus 1999] and those that are used when traces are held in memory for analysis, such as the timestamped representations of control flow traces [Y. Zhang and Gupta 2001] and dependence traces [X. Zhang and Gupta 2004].…”

“…Such annotated reperesentations are very useful when these dependences have to be stored in memory for analysis and have been discussed in Y. Zhang and Gupta [2001] and X. Zhang and Gupta [2004].…”

Seekable Compressed Traces

“…observe that the compressed form of traces is inefficient for many types of analyses, specifically those that target specific functions. Timestamped WPPs [33] use Sequitur to create path traces that correspond to individual function calls, and all path traces for a given function are stored together. This technique greatly improves spatial accessibility in traces, but compression rates are about 4 times worse than regular WPPs.…”

Dependable software needs pervasive debugging

“…Larus' whole program paths [10], and the extensions proposed by Zhang and Gupta [19] represent the state of the art, recording the complete control-flow history of a single thread in a reasonably compact form. An alternative combines logging with re-execution, typically recording information during 'forwards' execution and using this to recover intermediate states during 'reverse' execution.…”