A Taxonomy of Execution Replay Systems

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A Taxonomy of Execution Replay Systems

• Frank Cornelis
• Andy Georges
• Mark Christiaens
• Michiel Ronsse
• Tom Ghesquiere
• Koen De Bosschere
• Dept. ELIS
• Ghent University

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The Debugging Problem

• The debugging process is hard to automate
• Current tools are inadequate for debugging large
  scale, interactive, multi-threaded, and
  event-driven applications
• Hard to find bugs
• Synchronization errors
• Memory leaks
• Data races
• Dangling pointers

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Inadequate Tools

• Most common debugging technique cyclic debugging
  
• Problem there is no guarantee that the same
  behavior is observed during subsequent runs as
  many applications are non-deterministic
• Ideal situation reverse execution

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Solution Execution Replay
Execution 1
Execution 2
Trace file
record
replay
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Requirements

• Record must have low intrusion
• Replay must be accurate
• Record phase must be space efficient
• Replay phase must be time efficient

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Instant Replay
Compressed differences
JaRec
Tornado
Igor
RSA
Output Replay
jRapture
Recap
Input Replay
RecPlay
Scheduling Replay
DejaVu
Interrupt Replay
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Outline

• Introduction
• Content-based vs. ordering-based
• Dealing with input
• Dealing with timing
• Dealing with other processors
• Conclusion

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Content-based

• Record input for every instruction

r1 10 r1 11 r2 401 r111
add r1,1 ? r1 load 8(r1) ? r2 store r2 ?
12(r1)
Instruction can be executed in isolation Huge
trace files
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Ordering-based

• Record control flow of program from a given
  initial state

C1 C2
Smaller trace files Reexecution required
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Sources of non-determinism

• Input (e.g. a database, time, pixel coordinates)
• Timing (e.g. interrupts, scheduler actions)
• Interaction with other processors (processor,
  DMA, coprocessor)

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Outline

• Introduction
• Content-based vs. ordering-based
• Dealing with input
• Dealing with timing
• Dealing with other processors
• Conclusion

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Input instructions
application
Tornado jRapture
IO-instructions
? content-based

• content-based
• ordering-based

System calls
kernel
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Outline

• Introduction
• Content-based vs. ordering-based
• Dealing with input
• Dealing with timing
• Dealing with other processors
• Conclusion

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Dealing with timing

• Interrupts
• Input/output (timing aspect not input aspect)
• Scheduling

application
?ordering-based
other code
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How to determine the ordering

• PC is not enough
• Need extra counter SIC1
• Instructions executed
• No of backward jumps

Interrupt replay Repeatable scheduling DejaVu
1 Software Instruction Counter
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Outline

• Introduction
• Content-based vs. ordering-based
• Dealing with input
• Dealing with timing
• Dealing with other processors
• Conclusion

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Dealing with other processors

• Multi-threading (multiple threads in one address
  space)
• Multi-processing (multiple processes sharing a
  common block of memory)
• A coprocessor (video, DMA, )

c2
c1
c2
c1
Code 1
Code 2
data
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Many systems

• RecPlay
• Ordering-based up to the first data race
• JaRec
• Ordering-based up to the first data race
• IGOR
• Content-based checkpointing
• Recap
• Content-based reverse execution
• Instant Replay
• Ordering-based version numbers
• Netzerss approach
• Ordering-based also replays data races

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Overview
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Conclusion

• No execution replay system deals with all forms
  of non-determinism
• The more accurate the system gets, the more
  resources it needs (time, space), and hence
  becomes less useful
• There is a need for stable and platform-independen
  t tools to further support debugging