Low-Cost, Concurrent Checking of Pointer and Array Accesses in C Programs

Execution Shadow processing was motivated, in part, by a tool called AE that supports abstract execution [17]. AE is used for efficient generation of detailed program traces. A source program, in C, is instrumented to record a small set of key events during execution. After execution these events serve as input to an abstract version of the original program that can recreate a full trace of the original program. The events recorded by the original program include control flow decisions. These are essentially the same data needed by a shadow process to follow a main process. AE is a post-run technique that shifts some of the costs involved in tracing certain incidents during a program’s execution to the program that uses those incidents. In contrast, shadow processing is a run-time technique that removes expensive tracing from the critical execution path of a program and shifts it to another processor. Table 7: Concurrent Guarding using Shadow Processing: (user + system) time Program Original (time in seconds) Embedded Checking Shadow Guarding Purified (% increase) Guarded (% increase) Main (% increase) Shadow: without output calls (% increase) alvinn (50 epochs) 25.6 s 774.6% 472.3% < 1% 472.3% compress 2.9 s 748.3% 113.8% 10.3% 89.7% decompress 2.0 s 765.0% 145.0% 10.0% 85.0% ear 305.4 s 589.1% 642.0% < 1% 636.4% eqntott 18.8 s 735.6% 1337.2% 3.2% 1328.2% espresso 7.9 s 1107.6% 648.1% 1.3% 650.6% sc (loadc2) 38.6 s 613.5% 173.3% 6.7% 95.1% xlisp 122.1 s 988.1% 775.6% 5.6% 787.6%