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Tru64 UNIX
Kernel Debugging
Part Number: AA-RH99A-TE
July 1999
Product Version: Tru64UNIX Version 5.0or higher
Thismanualexplainshowtousetoolstodebugakernelandanalyzea
crashdumpoftheTru64UNIX(formerlyDIGITALUNIX)operating
system.Also,thismanualexplainshowtowriteextensionstothekernel
debuggingtools.
Compaq Computer Corporation
Houston, Texas
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©1999CompaqComputerCorporation COMPAQandtheCompaqlogoRegisteredinU.S.PatentandTrademarkOffice. AlphaandTru64are trademarksofCompaqInformationTechnologiesGroup,L.PintheUnitedStatesandothercountries. MicrosoftandWindowsaretrademarksofMicrosoftCorporationintheUnitedStatesandothercountries. UNIXandTheOpenGrouparetrademarksofTheOpenGroup.Allotherproductnamesmentionedherein maybetrademarksoftheirrespectivecompanies. Confidentialcomputersoftware. ValidlicensefromCompaqrequiredforpossession,use,orcopyin
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Contents About This Manual 1 Introduction to Kernel Debugging 1.1 LinkingaKernelImageforDebugging............................ 1–1 1.2 DebuggingKernelPrograms ........................................ 1–3 1.3 DebuggingtheRunningKernel..................................... 1–3 1.4 AnalyzingaCrashDumpFile ...................................... 1–5 2 Kernel Debugging Utilities 2.1 ThedbxDebugger .................................................... 2–2 2.1.1 InvokingthedbxDebuggerforKernelDebugging ...
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2.2.3.9 DisassemblingInstructions ................................ 2–21 2.2.3.10 DisplayingRemoteExportedEntries .................... 2–21 2.2.3.11 DisplayingtheFileTable .................................. 2–21 2.2.3.12 DisplayingtheudbandtcbTables........................ 2–22 2.2.3.13 PerformingCommandsonLists .......................... 2–22 2.2.3.14 DisplayingthelockstatsStructures ...................... 2–24 2.2.3.15 DisplayinglockinfoStructures ............................ 2–25 2.2.3.16 Disp
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3.2.7 CheckingArgumentsPassedtoanExtension ............... 3–7 3.2.8 CheckingtheFieldsinaStructure............................ 3–7 3.2.9 SettingthekdbxContext ....................................... 3–8 3.2.10 PassingCommandstothedbxDebugger..................... 3–9 3.2.11 DereferencingaPointer ......................................... 3–9 3.2.12 DisplayingtheErrorMessagesStoredinFields ............ 3–10 3.2.13 ConvertingaLongAddresstoaStringAddress ............ 3–10 3.2.14 FreeingMemory .......
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A Output from the crashdc Command Index Examples 3–1 TemplateExtensionUsingLists.................................... 3–23 3–2 ExtensionThatUsesLinkedLists:callout.c ..................... 3–24 3–3 TemplateExtensionsUsingArrays ................................ 3–27 3–4 ExtensionThatUsesArrays:file.c................................. 3–28 3–5 ExtensionThatUsesGlobalSymbols:sum.c..................... 3–34 Figures 2–1 UsingaGatewaySystemDuringRemoteDebugging........... 2–38 Tables 2–1 ThedbxAddressMod
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About This Manual Thismanualprovidesinformationonthetoolsusedtodebugakerneland analyzeacrashdumpfileoftheTru64™UNIX(formerlyDIGITALUNIX) operatingsystem. Italsoexplainshowtowriteextensionstothekernel debuggingtools. Youcanuseextensionstodisplaycustomizedinformation fromkerneldatastructuresoracrashdumpfile. Audience Thismanualisintendedforsystemprogrammerswhowriteprogramsthat usekerneldatastructuresandarebuiltintothekernel. Itisalsointended forsystemadministratorswhoareresponsibleformanagingtheop
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Organization Thismanualconsistsoffourchaptersandoneappendix: Chapter1 Introduces the concepts of kernel debugging and crash dump analysis. Describes the tools used to debug kernels and Chapter2 analyze crash dump files. Chapter3 Describeshowtowritea kdbxdebuggerextension. This chapterassumesyouhavepurchasedandinstalledaTru64 UNIXSourceKitandsohaveaccesstosourcefiles. Chapter4 Providesbackgroundinformationusefulforandexamples of analyzing crashdump files. AppendixA Containsexampleoutputfromthe cr
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G Manuals for general users S Manualsforsystemandnetworkadministrators P Manuals for programmers R Manualsforreferencepage users Somemanualsinthedocumentationhelpmeettheneedsofseveral audiences. Forexample,theinformationinsomesystemmanualsisalso usedbyprogrammers. Keepthisinmindwhensearchingforinformation onspecifictopics. TheDocumentationOverviewprovidesinformationonallofthemanualsin theTru64UNIXdocumentationset. Reader’s Comments Compaqwelcomesanycommentsandsuggestionsyouhaveonthisand otherTru
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% $ ApercentsignrepresentstheCshellsystemprompt. Adollarsignrepresentsthesystempromptforthe Bourne,Korn,andPOSIXshells. # Anumbersignrepresentsthesuperuserprompt. % cat Boldfacetypeininteractiveexamplesindicates typeduserinput. file Italic(slanted)typeindicatesvariablevalues, placeholders,andfunctionargumentnames. [|] {|} Insyntaxdefinitions,bracketsindicateitemsthat areoptionalandbracesindicateitemsthatare required. Verticalbarsseparatingitemsinside bracketsorbracesindicatethatyouchooseoneitem
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1 Introduction to Kernel Debugging Kerneldebuggingisatasknormallyperformedbysystemsengineerswriting kernelprograms. Akernelprogramisonethatisbuiltaspartofthekernel andthatreferenceskerneldatastructures. Systemadministratorsmight alsodebugthekernelinthefollowingsituations: • Aprocessishungorstopsrunningunexpectedly • Theneedarisestoexamine,andpossiblymodify,kernelparameters • Thesystemitselfhangs,panics,orcrashes Thismanualdescribeshowtodebugkernelprogramsandthekernel.Italso includesinformationab
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textfilethatdescribesthehardwareandsoftwarethatwillbepresenton therunningsystem. Usingthisinformation,thebootstraplinkerlinksthe modulesthatareneededtosupportthishardwareandsoftware.Thelinker buildsthekerneldirectlyintomemory. Youcannotdirectlydebugabootstrap-linkedkernelbecauseyoumustsupply thenameofanimagetothekerneldebuggingtools.Withouttheimage,the toolshavenoaccesstosymbolnames,variablenames,andsoon.Therefore, thefirststepinanykerneldebuggingeffortistodeterminewhetheryour kernelwaslinkedatb
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1.2 Debugging Kernel Programs Kernelprogramscanbedifficulttodebugbecauseyounormallycannot controlkernelexecution. Tomakedebuggingkernelprogramsmore convenient,thesystemprovidesthe kdebugdebugger. The kdebug debuggeriscodethatresidesinsidethekernelandallowsyoutousethedbx debuggertocontrolexecutionofarunningkernelinthesamemanneras youcontrolexecutionofauserspaceprogram. Todebugakernelprogram inthismanner,followthesesteps: 1. Buildyourkernelprogramintothekernelonatestsystem. 2. Setupthe kdebugdebug
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# dbx -k /vmunix /dev/mem Thiscommandinvokes dbxwiththekerneldebuggingflag, −k,which mapskerneladdressestomakekerneldebuggingeasier.The/vmunixand /dev/memparameterscausethedebuggertooperateontherunningkernel. Onceinthedbxenvironment,youusedbxcommandstodisplayprocessIDs andtraceexecutionofprocesses.Youcanperformthesametasksusingthe kdbxdebugger. Thefollowingexampleshowsthedbxcommandyouuseto displayprocessIDs: (dbx) kps PID COMM 00000 kernel idle 00001 init 00014 kloadsrv 00016 update . . . Ifyouw
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1.4 Analyzing a Crash Dump File Ifyoursystemcrashes,youcanoftenfindthecauseofthecrashbyusing dbxorkdbxtodebugoranalyzeacrashdumpfile. Theoperatingsystemcancrashbecauseoneofthefollowingoccurs: • Hardwareexception • Softwarepanic • Hungsystem Whenasystemhangs,itisoftennecessarytoforcethesystemtocreate dumpsthatyoucananalyzetodeterminewhythesystemhung. The SystemAdministrationmanualdescribestheprocedureforforcinga crashdumpofahungsystem. • Resourceexhaustion Thesystemcrashesorhangsbecauseitcannotco
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Atsystemreboottime,thecopyofcorememorysavedintheswappartitions iscopiedintoafile,calledacrashdumpfile. Youcananalyzethecrash dumpfiletodeterminewhatcausedthecrash.Bydefault,thecrashdumpis apartial(ratherthanfull)dumpandisincompressedform. Forcomplete informationaboutmanagingcrashdumpsandcrashdumpfiles,including howtochangedefaultsettings,seetheSystemAdministrationmanual.For examplesofanalyzingcrashdumpfiles,seeChapter4. 1–6 Introduction to Kernel Debugging
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2 Kernel Debugging Utilities TheTru64UNIXsystemprovidesseveraltoolsyoucanusetodebugthe kernelandkernelprograms.TheLadebugdebugger(availableasanoption) isalsocapableofdebuggingthekernel. Thischapterdescribesthreedebuggersandautilityforanalyzingcrash dumps: • Thedbxdebugger,whichisdescribedforkerneldebugginginSection2.1. (Forgeneraldbxuserinformation,seetheProgrammer’sGuide.) Youcanusethedbxdebuggertodisplaythevaluesofkernelvariables andkernelstructures. However,youmustunderstandthestructures andb
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______________________ Note _______________________ StartingwithTru64UNIXVersion5.0,allthepreviously mentionedtoolscanbeusedwithcompressed(vmzcore.n)and uncompressed(vmcore.n)crashdumpfiles. Olderversionsof thesetoolscanreadonly vmcore.nfiles. Ifyouareusingan olderversionofatool,usetheexpand_dumputilitytoproduce a vmcore.nfilefroma vmzcore.nfile. Formoreinformation aboutcompressedanduncompressedcrashdumpfiles,see expand_dump(8)andtheSystemAdministrationmanual. 2.1 The dbx Debugger The dbxdebugge
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• Thesystemcorememoryimage Thesefilesmaybefilesfromarunningsystem,suchas /vmunixand /dev/mem,ordumpfiles,suchasvmunix.nandvmzcore.n(compressed) orvmcore.n(uncompressed). Bydefault,crashdumpfilesarecreatedin the/var/adm/crashdirectory(seetheSystemAdministrationmanual). ______________________ Note _______________________ Youmightneedtobethesuperuser(rootlogin)toexaminethe runningsystemorcrashdumpfilesproducedby savecore. Whetheryouneedtobethesuperuserdependsonthedirectory andfileprotectionsforthef
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wanttoaddasymboltabletoyourcurrentdebuggingsessionratherthan endthesessionandstartanewone. Toaddasymboltabletoyourcurrent debuggingsession,followthesesteps: 1. Gotoawindowotherthantheoneinwhichthedebuggerisrunning, orputthedebuggerinthebackground,andrebuildthemodulesfor whichyouneedasymboltable. 2. Oncethemodulesbuildcorrectly,usetheostripcommandtostripa symboltableoutoftheresultingexecutablefile. Forexample,ifyour executablefileisnamed kernel_program,issueacommandsuchas thefollowingone: % /usr/
