VS Debugging Tricks

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Visual Studio undocumented native debugging tricks presentation. By Ofek Shilon.

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  • C++התחלות שלא הבשילו בזמןמקור עיקרי – בלוגים של מפתחי VSדברים מאד שימושיים – לחלק שמתי בקשות להפוך לפיצ'רים רשמייםVS2010 / VS2011B
  • Many people think that editing variables is the most they can intervene with the debugeeEdit variables, move execution around
  • אינליין – רלבנטי בRELEASE
  • Break *before* code change, greatly reduces the chance of stale codeUse directX sample!
  • Incremental linking: pads functions code, contains jump thunks to handle function relocationInconsistent with /OPT:REF, /OPT:ICF, /ORDER, /RELEASE, /FORCESome changes are too great, full linking occurs.All options are on by default in debug
  • 2005: for all users
  • comment std::vector רפרוף בסיסי על הסינטקס, רפרנסים טובים בסוףInsert carray childrenCarray previewVect3d preview
  • טוב גם לבדוק שם אם נדמה שלא פועל
  • כשיודעים מה לחפש – מוצאים המון
  • לא מוחבא ברג'יסטרי, יש UI, אבל במקום ממש לא סביר ורחוק מאד מVS עצמוהועף ב2005, הוחזר ב2008 לקול מחאות הציבור
  • Code: ::DeleteFile, GetLastError$fs fakes it...(int*)($fs)+0x18(int*)($tib)+0x34$errFormatting strings:12.3412.34,g$err,hr(_TEB*)$tib
  • HRESULT customization doesn’t even require debugger restart!!_TEB is not defined publically, but the debugger is aware of it. Contains much useful data for advanced scenarios (fiber-specific data, etc)
  • Doesn’t work for templated classes/methodsDoesn’t extend to wildcards/regexGood way to find entry points
  • No ‘name’ slot in TEB
  • Write-to BPs are implemented in hardware – dedicated x86 debug registers.Read-from debugs registers are available too, but were never exposed in VS.Some code required Maybe historical portability constraints? Dunno4 very similar implementations
  • Not investigating code *flow* - static feature.After /d1reportSingleClassLayout, type immediatelly your classTest: /d1reportSingleClassLayoutCDialog . show vftable, alignment, adjustorsDebug ODR violationsOptimize storageGain deep insightSince VS2010, collides with /showIncludes (?)Watch out for PCH – if your class definition isn’t compiled, its layout won’t be shown
  • $cmdline credit: John Cunningham, http://blogs.msdn.com/b/ms_joc/archive/2004/08/23/218912.aspx$env=0 no longer works in VS2010
  • Demo – on envvars.S -U 0x006fdad0 60 "ALLUSERSPROFILE"שימושי בדיבוג של דמפים מלאים
  • VS Debugging Tricks

    1. 1. Little KnownNative Debugging Tricks Ofek Shilon Director of Algorithms @ Sarin Technologies www.thetweaker.wordpress.com
    2. 2. DISCLAIMER
    3. 3. VS AS AN INTERPRETER
    4. 4. Expression Evaluator• Demo• Scope – Watch, QuickWatch, – Immediate, – BP conditions, ‘when hit’• Call Functions from the debugger!
    5. 5. Expression Evaluator• Context Operator – Documentation is wrong. – Might require decorated names. – VS2010 blocked WIN-API, but eased usage of others. – VS11B supports the simpler syntax msvcr110d.dll!fabs(-8.0f)
    6. 6. Expression Evaluator• Thread context• Access insensitive• Blind to inlined functions• Things to try when evaluation fails: – Very explicit casting, – Explicit addresses.
    7. 7. Edit and Continue• Demo• Stale code
    8. 8. Edit and Continue• Preparation: /ZI, /INCREMENTAL
    9. 9. Edit and Continue• Limitations: – Inconsistent with /RELEASE, /OPT:REF, /OPT:ICF, /ORDER, /FORCE, – Does not invoke custom build steps, – Isn’t supported on attached processes, – Can’t change object layout, – Doesn’t regenerate IDL files, – Can’t change resource files, – Does not build static libs.
    10. 10. CLICK SAVERS
    11. 11. StepOver• Demo
    12. 12. StepOver• VC6: autoexp section [ExecutionControl]• VC7: Reg key - HKCUSoftwareMicrosoftVisualStudio7.0NativeDEStepOver• VC8: HKLMSoftwareMicrosoftVisualStudio8.0NativeDEStepOver• VC10, VC11B: HKCUSoftwareMicrosoftVisualStudio10.0_ConfigNativeDEStepOver Dropped ‘=NoStepInto’ syntax
    13. 13. StepOver• Warning! When 2 or more instances of VS are active, occasionally it would create and use a duplicate reg key … and all ’10.0_Config’ modifications would have no effect !
    14. 14. StepOver• Credit: Andy Pennell http://blogs.msdn.com/b/andypennell/archive/2004/02/06/69004.aspx• A request to make StepOver official: http://visualstudio.uservoice.com/forums/121579-visual- studio/suggestions/2668765-support-nostepinto-registry-mechanism
    15. 15. autoexp• How’s the debugger ‘aware’ of STL containers?• autoexp.dat – By default at %VS folder %Common7PackagesDebugger
    16. 16. autoexp• Demo• Specialized syntax for common containers: Array, List, Map, Tree.• Re-parsed on every debugging session• Extremely fragile, yet excellent investment
    17. 17. autoexp• Status limbo:
    18. 18. autoexp• Bypass file path via env var: _vcee_autoexp• Bypass visualizer locally: xxx,!• Bypass globally in Tools/Options:
    19. 19. autoexp• Resources: – Avery Lee http://virtualdub.org/blog/pivot/entry.php?id=120 – Stephan T. Lavavej BoostCon presentation http://filetolink.com/d/?h=a456fc7fd3d35644edcbe5e764d1ba63&t=1315076450&f=17ad36ef – My blog: complete MFC containers visualization, Matrix 2D visualization, and more www.thetweaker.wordpress.org – A request to make autoexp official: http://visualstudio.uservoice.com/forums/121579-visual- studio/suggestions/2056273-support-debug-visualizers-through- autoexp-dat
    20. 20. Sound Alerts• Win7: Control Panel Hardware and Sounds Sound Change system sounds• WinXP: Control Panel Sounds and Audio... Program Events – Microsoft Developer
    21. 21. TRACING ERRORS
    22. 22. GetLastError Interactively• GetLastError implementation:• (int*)($fs)+0x34• (int*)($tib)+0x34• $err !• Credit: msdn http://msdn.microsoft.com/en-us/library/dtw169z6.aspx
    23. 23. Extensions• Customizing ‘,hr’ display in autoexp.dat:• Other TEB data: (_TEB*)$tib
    24. 24. Breaking on Errors• BP location: (int*)($tib)+0x34• Specific error: BP condition – Slooooooooow• g_dwLastErrorToBreakOn ! – (int*){,,ntdll.dll}_g_dwLastErrorToBreakOn – Fails in VC10 over Win7. Restored in VC11B• Credit: Daniel Pearson, http://blogs.msdn.com/b/danpear/archive/2007/04/06/2033100.aspx
    25. 25. INVESTIGATING CODE
    26. 26. Breaking on all class methods• Break at function: Class::*• Credit: Habib Heydarian http://blogs.msdn.com/b/habibh/archive/2009/09/10/class-breakpoint- how-to-set-a-breakpoint-on-a-c-class-in-the-visual-studio-debugger.aspx
    27. 27. Naming Native Threads• Demo• ‘Documented hack’ Credit: MSDN http://msdn.microsoft.com/en-us/library/xcb2z8hs.aspx
    28. 28. Breaking on Data Read• Some code required.• Links to 4 implementations: http://thetweaker.wordpress.com/2011/05/22/breaking-on-data-read/• Request to make it official: http://visualstudio.uservoice.com/forums/121579-visual- studio/suggestions/2668700-expose-break-on-read-breakpoints
    29. 29. Static Object Layout• /d1reportSingleClassLayout• /d1reportAllClassLayout• Credit: Andy Rich http://blogs.msdn.com/b/vcblog/archive/2007/05/17/diagnosing-hidden- odr-violations-in-visual-c-and-fixing-lnk2022.aspx
    30. 30. ENHANCED DIAGNOSIS
    31. 31. Useful Pseudo-registers• $tid -> very useful as a BP condition.• $env=0 -> view debugee environment variables – In VC11: just $env in watch• $cmdline = 0 -> view launching command line Credit: John Cunningham, http://blogs.msdn.com/b/ms_joc/archive/2004/08/23/218912.aspx
    32. 32. Useful Pseudo-registers• $handles -> narrows down handle leaks• $clk -> rough profiling• $user -> view permissions info• Credits: Steve Steiner, Gregg Miskelly, et. al. http://blogs.msdn.com/b/stevejs/ http://blogs.msdn.com/b/greggm/
    33. 33. Searching Through Memory• Credit: msdn http://msdn.microsoft.com/en-us/library/ms171363.aspx
    34. 34. www.thetweaker.wordpress.comofekshilon@gmail.com THANK YOU.

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