Towards Effective Runtime Trace Generation Techniques in the 'NET Framework

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Towards Effective Runtime Trace Generation
Techniques in the .NET Framework

• Krisztián Pócza, Mihály Biczó, Zoltán Porkoláb
• Eötvös Loránd University, Budapest
• Faculty of Informatics
• Department of Programming Languages and Compilers

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The structure of this presentation

• Motivation, problem statement
• Tools .NET Debugging and Profiling
  Infrastructure
• Trace generation using the debugger
• Trace generation using the profiler
• Comparing the methods
• Future work

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Motivation, problem statement

• Usage in industry
• Generate runtime trace during execution
• Real-world applications in production environment
• Non-intrusive
• No development environment allowed
• No debugging capabilities (no side effects)
• No human interaction
• Error detection
• Usage in academy
• Generate trace for program slicing
• Identify statements that affect a variable at a
  given program location

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.NET Debugging and Profiling Infrastructure

• Design time interface
• Debugging events
• Different process
• Notifications
• Symbol manager
• Interprets PDB files
• Identification of program elements

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.NET Debugging and Profiling Infrastructure

• Publisher
• Enumerates runningmanaged processesin the
  system
• Profiler
• Events
• Resource usage, CLR events (JIT, Load, GC, memory
  allocation, exceptions, etc.)

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Trace generation using the debugger

• Based on MDbg (corapi2, corapi)
• Steps
• Create process under the control of the debugger
• Set a breakpoint at the program entry point
• Start the application
• After reaching the breakpoint do Step-in
  operations

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Trace generation using the debugger

• What a debugging event (Step-in, breakpoint
  reached) does
• Sets evtComplete AutoResetEvent
• Waits for evtModState AutoResetEvent
• What the main program does in a while loop
• Waits for evtComplete AutoResetEvent
• Generates trace about the current sequence point
• Sets evtModState AutoResetEvent
• Download
• http//avalon.inf.elte.hu/src/netdebug/default.asp
  x

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Trace generation using the profiler

• Technical background
• In-process
• Implement a COM interface in C to handle
  profiler events
• Environment variables must be set
• The assembly metadata should be extended when
  loaded
• Reference for methods generating trace - Tokens
• ModuleLoadFinished profiler event
• Requires IL Code Rewriting

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Trace generation using the profiler

• ClassLoadFinished
• Profiler event
• Visit all methods of theclass and rewrite
• Method types
• Tiny
• Fat
• IL Instruction types
• No parameter, one integer parameter, token
  parameter, multiple parameters
• Exception Handling Clauses (EHC)
• Try, catch, finally

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Trace generation using the profiler

• Code Rewriting steps
• Query IL Code binary data
• Break it at sequence points
• Parse binary data and store it in custom data
  structures (binary representation of every IL
  instruction)
• Upgrade method and instruction format ()
• Insert instrumentation code at every sequence
  point()
• Recalculate offsets and lengths ()
• Store the new representation in binary format

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Trace generation using the profiler

• Upgrade method and instruction format
• Problems while inserting new IL instructions
• Can break the limitations of tiny methods
• Short branch instructions maximum relative
  length can be too short
• EHCs representation of offset and length
  limitation can be too restrictive
• Solution
• Upgrade method format
• Convert short branch instructions to long branch
  instructions
• Store EHCs offset and length in DWORD instead of
  BYTE or WORD

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Trace generation using the profiler

• Insert instrumentation code at every SP
• Template
• Substitute
• 1-4 bytes, 6-9, etc. bytes with current line and
  column numbers

BYTE insertFuncInst31 insertFuncInst0
0x20 //ldc.i4, start line insertFuncInst5
0x20 //ldc.i4, start column insertFuncInst10
0x20 //ldc.i4, end line insertFuncInst15
0x20 //ldc.i4, end column insertFuncInst20
0x20 // ldc.i4, func. id insertFuncInst25
0x0 // ldc.i4.1 or ldc.i4.2 insertFuncInst26
0x28 // call ((DWORD )(insertFuncInst27))
tracerDoFuncMethodTokenID
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Trace generation using the profiler

• Recalculate offsets and lengths
• Recalculate method length
• Recalculate branch relative offsets
• Point to the first instruction of the new
  sequence point if pointed to the first
  instruction of the old one
• Point to the same instruction of the new sequence
  point if pointed to the not first instruction of
  the old one
• Recalculate EHCs offset and length

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Comparing the methods

• None of them require us to modify the original
  source code
• Differences

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Comparing the methods

• Test results
• Advance with the Profiler

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Future work

• Variables of different types
• Almost finished
• Exception handling
• Anonymous methods
• Generic types
• Application domains
• Integrate with program slicing

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Demo
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• QA

Krisztián Pócza kpocza_at_kpocza.net
Mihály Biczó mihaly.biczo_at_axelero.hu
Zoltán Porkoláb gsd_at_elte.hu