Dependable computing needs pervasive debugging Tim Harris [e-mail]

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Dependable computing needs pervasive debugging
Tim Harristim.harris_at_cl.cam.ac.uk
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Outline

• Motivation
• Problems with existing debuggers
• Pervasive debugging
• System architecture
• Demo

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Motivation

• One of the projects weve been working on is
  building lock-free data structures
• Safe for multi-threaded use, but dont use locks
• Built from atomic read, write and CAS lots of
  subtle interactions
• Algorithms are short, but formal methods hard to
  apply here

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Debugger problems

• Usually only forward execution
• Probe effects / heisenbugs
• e.g. relaxed memory orderings or
  genuine-parallelism versus time-sliced
• Support for concurrency
• e.g. deterministic re-execution
• Support for distribution
• usually one debugger needed for each process
• sometimes support for tracing across RPCs
• network monitoring software, tcpdump, nProbe

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Pervasive debugging

• Present the user with a single interface to the
  entire system
• All of the processes involved
• All of the threads within them
• All of the communication links
• Execute the application in a virtualized and
  completely deterministic environment
• At least wed have bohrbugs rather than heisen-
  ones
• Challenges
• Correspondence between the real and virtual
  environments
• Design of internal interfaces
• Implementation efficiency

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System architecture
Pervasive debugger
User interface
CurrentlyGDB
Executiondriver
Remote stub
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Demo
CPU
CPU
Sharedmemory