LBA Reading Group Review:

HeapMon: A helper-thread approach to programmable, automatic, and low-overhead memory bug detection

Software View

Hardware View

Results

Details

SESC Simulator - UIUC - MIPS ISA

More…

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

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)

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