1. LBA Reading Group Review: HeapMon: A helper-thread approach to programmable, automatic, and low- overhead memory bug detection

2. Software View

3. Hardware View

4. Results

5. Details SESC Simulator - UIUC - MIPS ISA

6. More…

7. Key Take-Aways: Strengths Heap access checking with low performance overhead Filter bits can provide enormous benefit  95% of checks eliminated But… filter bit calculation is expensive  Checks the effect of the access  Improves queue size as well as performance 64-entry request and 8-entry response Two modes: precise and imprecise Sensitivity analysis shows VFC key for some apps Cute discussion of undetected, injected bugs

8. Key Take-Aways: Weaknesses Hardware non-neglible (VFC, filter bits, queue) Similar MemCheck limitations  Unable to detect OOB accesses that hit an allocated area  Apps that perform special mem. management need handling  Other? What about stack accesses?  Possible by treating frame creation as malloc? No discussion of false positives No discussion of protections for checking mechanism  The “stop-monitoring” annotation could be dangerous No discussion of precisely clearing the filter bits Unclear how to generalize (eg TaintCheck) Precise mode modeled sufficiently? (single-cycle fetch)

9. Comparisons CMP parallel always-on bug checking SW event insertion similar to annotations Application core stalls if queue is full No discussion of multi-level state bit checking* No handling of memory ordering resolution