The Art of Debugging: with GDB, DDD, and Eclipse

280 Pages·2008·9.347 MB·English

by  Norman Matloff, Peter Jay Salzman

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Debugging is crucial to successful software develop- • Use features like catchpoints, convenience variables,
ment, but even many experienced programmers find and artificial arrays IIEE WWIITTHH GGDDBB,, DDDDDD,,
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it challenging. Sophisticated debugging tools are • Avoid common debugging pitfalls HH A A
available, yet it may be difficult to determine which
features are useful in which situations. The Art of Real world examples of coding errors help to clarify the GGRR AANNDD EECCLLIIPPSSEE
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Debugging is your guide to making the debugging authors’ guiding principles, and coverage of complex TT
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process more efficient and effective. topics like thread, client-server, GUI, and parallel
The Art of Debugging illustrates the use three of the most programming debugging will make you even more , D, D O O
proficient. You’ll also learn how to prevent errors in the
popular debugging tools on Linux/Unix platforms: GDB, DDFF
first place with text editors, compilers, error reporting, N O R M A N M A T L O F F A N D P E T E R J AY S A L Z M A N
DDD, and Eclipse. The text-command based GDB (the DD
and static code checkers. DD
GNU Project Debugger) is included with most distributions. ,,
DDD is a popular GUI front end for GDB, while Eclipse Whether you dread the thought of debugging your A AEE
provides a complete integrated development environment. programs or simply want to improve your current NNBB
debugging efforts, you’ll find a valuable ally in The DD
In addition to offering specific advice for debugging with
Art of Debugging. UU
each tool, authors Norm Matloff and Pete Salzman cover EE
general strategies for improving the process of finding ABOUT THE AUTHORS CCGG
and fixing coding errors, including how to: LLGG
Norman Matloff, a computer science professor at UC II
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• Inspect variables and data structures Davis, is the author of several popular public-domain II
SS
software packages and online tutorials. NN GG
• Understand segmentation faults and core dumps EE
Peter Jay Salzman received his doctorate in theoretical GG
• Know why your program crashes or throws exceptions
physics at UC Davis and founded the Linux Users Group
DD
of Davis.
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THE ART OF DEBUGGING
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THE ART OF
DEBUGGING
with GDB, DDD, and Eclipse
by Norman Matloff and Peter Jay Salzman
SanFrancisco
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THEARTOFDEBUGGINGWITHGDB,DDD,ANDECLIPSE.Copyright©2008byNormanMatloffandPeter
JaySalzman.
Allrightsreserved.Nopartofthisworkmaybereproducedortransmittedinanyformorbyanymeans,electronic
ormechanical,includingphotocopying,recording,orbyanyinformationstorageorretrievalsystem,withoutthe
priorwrittenpermissionofthecopyrightownerandthepublisher.
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ISBN-10:1-59327-002-X
ISBN-13:978-1-59327-174-9
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LibraryofCongressCataloging-in-PublicationData
Matloff, Norman S.
The art of debugging with GDB, DDD, and Eclipse / Norman Matloff and P.J.
Salzman.
p. cm.
ISBN-13: 978-1-59327-002-5
ISBN-10: 1-59327-002-X
1. Debugging in computer science. 2. Computer software-Quality control. I.
Salzman, P.J. II. Title.
QA76.9.D43M35 2008
005.1’4-dc22
2003017566
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BRIEF CONTENTS
Preface............................................................................. xi
Chapter1:SomePreliminariesforBeginnersandPros................................... 1
Chapter2:StoppingtoTakeaLookAround............................................ 47
Chapter3:InspectingandSettingVariables............................................ 95
Chapter4:WhenaProgramCrashes .................................................117
Chapter5:DebugginginaMultiple-ActivitiesContext...................................145
Chapter6:SpecialTopics............................................................185
Chapter7:OtherTools...............................................................205
Chapter8:UsingGDB/DDD/EclipseforOtherLanguages...............................235
Index...............................................................................259
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CONTENTS IN DETAIL
PREFACE xi
1
SOME PRELIMINARIES FOR BEGINNERS AND PROS 1
1.1 DebuggingToolsUsedinThisBook .......................................... 1
1.2 ProgrammingLanguageFocus ............................................... 2
1.3 ThePrinciplesofDebugging................................................. 2
1.3.1 TheEssenceofDebugging: ThePrincipleofConfirmation........... 2
1.3.2 OfWhatValueIsaDebuggingToolforthePrincipleofConfirmation? 3
1.3.3 OtherDebuggingPrinciples...................................... 4
1.4 Text-Basedvs. GUI-BasedDebuggingTools,andaCompromiseBetweenThem... 5
1.4.1 BriefComparisonofInterfaces ................................... 5
1.4.2 Compromises................................................... 12
1.5 MainDebuggerOperations ................................................. 14
1.5.1 SteppingThroughtheSourceCode............................... 14
1.5.2 InspectingVariables ............................................ 15
1.5.3 Issuingan“AllPointsBulletin”forChangestoaVariable ........... 17
1.5.4 MovingUpandDowntheCallStack ............................. 17
1.6 OnlineHelp................................................................ 19
1.7 IntroductoryDebuggingSession.............................................. 19
1.7.1 TheGDBApproach............................................. 22
1.7.2 TheSameSessioninDDD ....................................... 36
1.7.3 TheSessioninEclipse........................................... 38
1.8 UseofStartupFiles ......................................................... 43
2
STOPPING TO TAKE A LOOK AROUND 47
2.1 MechanismsforPause ...................................................... 47
2.2 OverviewofBreakpoints .................................................... 48
2.3 KeepingTrackofBreakpoints................................................ 49
2.3.1 BreakpointListsinGDB.......................................... 49
2.3.2 BreakpointListsinDDD.......................................... 50
2.3.3 BreakpointListsinEclipse........................................ 51
2.4 SettingBreakpoints ......................................................... 51
2.4.1 SettingBreakpointsinGDB ...................................... 51
2.4.2 SettingBreakpointsinDDD ...................................... 55
2.4.3 SettingBreakpointsinEclipse .................................... 56
2.5 ExtendedGDBExample..................................................... 56
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2.6 PersistenceofBreakpoints ................................................... 59
2.7 DeletingandDisablingBreakpoints .......................................... 60
2.7.1 DeletingBreakpointsinGDB..................................... 61
2.7.2 DisablingBreakpointsinGDB.................................... 62
2.7.3 DeletingandDisablingBreakpointsinDDD ....................... 62
2.7.4 DeletingandDisablingBreakpointsinEclipse ..................... 63
2.7.5 “Moving”BreakpointsinDDD.................................... 64
2.7.6 Undoing/RedoingBreakpointActionsinDDD ..................... 66
2.8 MoreonViewingBreakpointAttributes ....................................... 67
2.8.1 GDB........................................................... 67
2.8.2 DDD........................................................... 69
2.8.3 Eclipse......................................................... 69
2.9 ResumingExecution......................................................... 69
2.9.1 InGDB ........................................................ 70
2.9.2 InDDD ........................................................ 78
2.9.3 InEclipse ...................................................... 79
2.10 ConditionalBreakpoints..................................................... 79
2.10.1 GDB........................................................... 80
2.10.2 DDD........................................................... 83
2.10.3 Eclipse......................................................... 84
2.11 BreakpointCommandLists................................................... 85
2.12 Watchpoints ............................................................... 89
2.12.1 SettingWatchpoints............................................. 90
2.12.2 Expressions .................................................... 93
3
INSPECTING AND SETTING VARIABLES 95
3.1 OurMainExampleCode.................................................... 95
3.2 AdvancedInspectionandSettingofVariables................................. 98
3.2.1 InspectioninGDB .............................................. 98
3.2.2 InspectioninDDD...............................................102
3.2.3 InspectioninEclipse.............................................103
3.2.4 InspectingDynamicArrays ......................................104
3.2.5 WhatAboutC++?..............................................109
3.2.6 MonitoringLocalVariables ......................................112
3.2.7 ExaminingMemoryDirectly......................................112
3.2.8 AdvancedOptionsforPrintandDisplay ..........................112
3.3 SettingVariablesfromWithinGDB/DDD/Eclipse..............................113
3.4 GDB’sOwnVariables ......................................................113
3.4.1 MakingUseoftheValueHistory .................................114
3.4.2 ConvenienceVariables..........................................114
4
WHEN A PROGRAM CRASHES 117
4.1 BackgroundMaterial: MemoryManagement..................................118
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4.1.1 WhyDoesaProgramCrash?....................................118
4.1.2 ProgramLayoutinMemory ......................................118
4.1.3 TheNotionofPages ............................................121
4.1.4 DetailsontheRoleofthePageTable .............................122
4.1.5 ASlightMemory-AccessBugMightNotCauseaSegFault .........124
4.1.6 SegFaultsandUnixSignals .....................................125
4.1.7 OtherTypesofExceptions .......................................128
4.2 CoreFiles..................................................................129
4.2.1 HowCoreFilesAreCreated.....................................129
4.2.2 YourShellMaySuppresstheCreationofaCoreFile...............130
4.3 ExtendedExample..........................................................131
4.3.1 FirstBug .......................................................135
4.3.2 Don’tLeaveGDBDuringaDebuggingSession ....................137
4.3.3 SecondandThirdBugs..........................................137
4.3.4 FourthBug .....................................................139
4.3.5 FifthandSixthBugs.............................................141
5
DEBUGGING IN A MULTIPLE-ACTIVITIES CONTEXT 145
5.1 DebuggingClient/ServerNetworkPrograms..................................145
5.2 DebuggingThreadedCode..................................................151
5.2.1 ReviewofProcessesandThreads.................................151
5.2.2 BasicExample..................................................153
5.2.3 AVariation ....................................................159
5.2.4 GDBThreadsCommandSummary ...............................161
5.2.5 ThreadsCommandsinDDD......................................161
5.2.6 ThreadsCommandsinEclipse ...................................161
5.3 DebuggingParallelApplications .............................................163
5.3.1 Message-PassingSystems........................................164
5.3.2 Shared-MemorySystems.........................................170
5.4 ExtendedExample..........................................................171
5.4.1 OpenMPOverview .............................................171
5.4.2 OpenMPExampleProgram......................................172
6
SPECIAL TOPICS 185
6.1 WhatIfItDoesn’tEvenCompileorLoad?.....................................185
6.1.1 PhantomLineNumbersinSyntaxErrorMessages ..................185
6.1.2 MissingLibraries................................................190
6.2 DebuggingGUIPrograms...................................................194
6.2.1 DebuggingCursesPrograms.....................................194
7
OTHER TOOLS 205
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7.1 MakingGoodUseofaTextEditor ...........................................206
7.1.1 SyntaxHighlighting .............................................206
7.1.2 MatchingBrackets ..............................................208
7.1.3 VimandMakefiles..............................................209
7.1.4 MakefilesandCompilerWarnings ...............................210
7.1.5 FinalThoughts onaTextEditorasanIDE .........................211
7.2 MakingGoodUseoftheCompiler...........................................212
7.3 ErrorReportinginC ........................................................213
7.3.1 Usingerrno ....................................................213
7.4 BetterLivingwithstraceandltrace ...........................................217
7.5 StaticCodeCheckers: lintandFriends........................................219
7.5.1 HowtoUsesplint...............................................221
7.5.2 LastWords.....................................................221
7.6 DebuggingDynamicallyAllocatedMemory ...................................221
7.6.1 StrategiesforDetectingDAMProblems ...........................224
7.6.2 ElectricFence ..................................................225
7.6.3 DebuggingDAMProblemswithGNUCLibraryTools ..............228
8
USING GDB/DDD/ECLIPSE FOR OTHER LANGUAGES 235
8.1 Java.......................................................................236
8.1.1 DirectUseofGDBforDebuggingJava............................238
8.1.2 UsingDDDwithGDBtoDebugJava..............................240
8.1.3 UsingDDDasaGUIforJDB.....................................241
8.1.4 DebuggingJavainEclipse.......................................241
8.2 Perl .......................................................................242
8.2.1 DebuggingPerlviaDDD ........................................244
8.2.2 DebuggingPerlinEclipse........................................246
8.3 Python.....................................................................247
8.3.1 DebuggingPythoninDDD.......................................249
8.3.2 DebuggingPythoninEclipse.....................................250
8.4 DebuggingSWIGCode ....................................................251
8.5 AssemblyLanguage ........................................................255
INDEX 259
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PREFACE
“Hey, this thing really works!” So said one of our stu-
dents, Andrew, after he made serious use of a debug-
ging tool for the first time. He had learned about de-
bugging tools three years earlier in his freshman pro-
gramming courses, but he had dismissed them as just
something to learn for the final exam. Now as a fourth-
year student, Andrew’s professor urged him to stop us-
ing print statements for debugging and make use of
formal debugging tools. To his delight and surprise,
he found that he could greatly reduce his debugging
time by making use of the proper tools.
Therearemany“Andrews”outthere,amongstudentsandamongwork-
ingprogrammers,andwehopethisbookwilltriggeran“Andrew-like”epiphany
forthem. Butevenmoreso,wehopetoreachthemanypeoplewhodouse
debuggingtoolsbutarenotsurewhatcanbedoneinspecializedsituations
andwhowouldliketolearnmoreaboutdebuggingtoolsandthephilosophy
behindthem.
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