Debugging: Difference between revisions

Revision as of 13:05, 29 April 2024

Latest revision as of 09:57, 22 August 2025

(26 intermediate revisions by 23 users not shown)

Line 1:

{{Short description|Process of finding and resolvingFixing defects or problems withinin aan computerengineered programsystem}}

{{Redirect|Debug}}

{{Software development process|Core activities}}

In [[computer programming]] and [[software developmentengineering]], '''debugging''' is the process of finding andthe resolving ''[[SoftwareRoot cause buganalysis|bugs]]''root (defects or problems that prevent correct operation) within [[computer programcause]]s, [[softwareworkaround]]s, orand possible fixes for [[Softwarebug system(engineering)|systembugs]]s.

DebuggingFor [[software]], debugging tactics can involve [[interactive]] debugging, [[control flow]] analysis, [[unit testing]], [[integration testing]], [[Logfile|log file analysis]], monitoring at the [[application monitoring|application]] or [[system monitoring|system]] level, [[memory dump]]s, and [[profiling (computer programming)|profiling]]. Many [[Programming language|programming languages]] and [[Programming tool|software development tools]] also offer programs to aid in debugging, known as ''[[debugger]]s''debuggers.

==Etymology==

Line 11:

[[File:First Computer Bug, 1945.jpg|thumb|A computer log entry from the Mark II, with a moth taped to the page]]

The term "''bug"'', in the sense of defect, dates back at least to 1878 when [[Thomas Edison]] wrote "little faults and difficulties" ofin mechanicalhis engineeringinventions as "Bugs".

A popular story from the 1940s is from [[Admiral Grace Hopper]].<ref>{{Cite web |url=https://books.google.com/books?id=JT0EAAAAMBAJ&pg=RA1-PA33 |title=InfoWorld Oct 5, 1981 |date=5 October 1981 |access-date=July 17, 2019 |archive-date=September 18, 2019 |archive-url=https://web.archive.org/web/20190918012636/https://books.google.com/books?id=JT0EAAAAMBAJ&pg=RA1-PA33&lpg=RA1-PA33&focus=viewport |url-status=live }}</ref>. While she was working on a [[Harvard Mark II|Mark II]] computer at Harvard University, her associates discovered a [[moth]] stuck in a relay that impeded operation and wrote in a log book "First actual case of a bug being found". Although probably a [[word play|joke]], conflating the two meanings of bug (biological and defect), the story indicates that the term was used in the computer field at that time.

Similarly, the term "''debugging"'' seems to have beenwas used as a term in aeronautics before entering the world of [[Computer|computers. In an interview Grace Hopper remarked that she was not coining the term.{{Citation needed|date=July 2015}} The moth fit the already existing terminology, so it was saved]]. A letter from [[J. Robert Oppenheimer]], (director of the [[WWII]] atomic bomb [[Manhattan Project]] at Los Alamos, New Mexico) used the term in a letter to Dr. [[Ernest Lawrence]] at UC Berkeley, dated October 27, 1944,<ref>{{Cite web |url=https://bancroft.berkeley.edu/Exhibits/physics/images/bigscience25.jpg |title=Archived copy |access-date=2019-12-17 |archive-date=2019-11-21 |archive-url=https://web.archive.org/web/20191121001830/https://bancroft.berkeley.edu/Exhibits/physics/images/bigscience25.jpg |url-status=live }}</ref> regarding the recruitment of additional technical staff.

The [[Oxford English Dictionary]] entry for "''debug"'' quotesuses the term "''debugging" used'' in reference to airplane engine testing in a 1945 article in the Journal of the Royal Aeronautical Society. An article in "Airforce" (June 1945 p.&nbsp;50) also refers to debugging, this time of aircraft cameras. Hopper's [[computer bug|bug]] was found on September 9, 1947. Computer programmers did not adopt the term until the early 1950s.

An article in "Airforce" (June 1945 p.&nbsp;50) refers to ''debugging'' aircraft cameras.

The seminal article by Gill<ref>S. Gill, [https://www.jstor.org/stable/98663 The Diagnosis of Mistakes in Programmes on the EDSAC] {{Webarchive|url=https://web.archive.org/web/20200306083748/https://www.jstor.org/stable/98663 |date=2020-03-06 }}, Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences, Vol. 206, No. 1087 (May 22, 1951), pp. 538-554</ref> in 1951 is the earliest in-depth discussion of programming errors, but it does not use the term "''bug"'' or "''debugging"''.

The [[Oxford English Dictionary]] entry for "debug" quotes the term "debugging" used in reference to airplane engine testing in a 1945 article in the Journal of the Royal Aeronautical Society. An article in "Airforce" (June 1945 p.&nbsp;50) also refers to debugging, this time of aircraft cameras. Hopper's [[computer bug|bug]] was found on September 9, 1947. Computer programmers did not adopt the term until the early 1950s.

The seminal article by Gill<ref>S. Gill, [https://www.jstor.org/stable/98663 The Diagnosis of Mistakes in Programmes on the EDSAC] {{Webarchive|url=https://web.archive.org/web/20200306083748/https://www.jstor.org/stable/98663 |date=2020-03-06 }}, Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences, Vol. 206, No. 1087 (May 22, 1951), pp. 538-554</ref> in 1951 is the earliest in-depth discussion of programming errors, but it does not use the term "bug" or "debugging".

In the [[Association for Computing Machinery|ACM]]'s digital library, the term "''debugging"'' is first used in three papers from the 1952 ACM National Meetings.<ref>Robert V. D. Campbell, [https://dl.acm.org/citation.cfm?id=609784.609786 Evolution of automatic computation] {{Webarchive|url=https://web.archive.org/web/20190918012641/https://dl.acm.org/citation.cfm?id=609784.609786 |date=2019-09-18 }}, Proceedings of the 1952 ACM national meeting (Pittsburgh), p 29-32, 1952.</ref><ref>Alex Orden, [https://dl.acm.org/citation.cfm?id=609784.609793 Solution of systems of linear inequalities on a digital computer], Proceedings of the 1952 ACM national meeting (Pittsburgh), p. 91-95, 1952.</ref><ref>Howard B. Demuth, John B. Jackson, Edmund Klein, N. Metropolis, Walter Orvedahl, James H. Richardson, [https://dl.acm.org/citation.cfm?id=808982 MANIAC] doi=10.1145/800259.808982, Proceedings of the 1952 ACM national meeting (Toronto), p. 13-16</ref> Two of the three use the term in quotation marks.

By 1963, "''debugging"'' was a common- enough term to be mentioned in passing without explanation on page 1 of the [[Compatible Time-Sharing System|CTSS]] manual.<ref>[http://www.bitsavers.org/pdf/mit/ctss/CTSS_ProgrammersGuide.pdf The Compatible Time-Sharing System] {{Webarchive|url=https://web.archive.org/web/20120527174321/http://www.bitsavers.org/pdf/mit/ctss/CTSS_ProgrammersGuide.pdf |date=2012-05-27 }}, M.I.T. Press, 1963</ref>

==Scope==

Line 40 ⟶ 43:

==Debugging process==

The debugging process normally begins with identifying the steps to reproduce the problem. This can be a non-trivial task, particularly with [[Parallel computing|parallel processes]] and some [[Heisenbug]]s for example. The specific [[user environment]] and usage history can also make it difficult to reproduce the problem.

After the bug is reproduced, the input of the program may need to be simplified to make it easier to debug. For example, a bug in a compiler can make it [[Crash (computing)|crash]] when parsing a large source file. However, after simplification of the test case, only few lines from the original source file can be sufficient to reproduce the same crash. Simplification may be done manually using a [[Divide-and-conquer algorithm|divide-and-conquer]] approach, in which the programmer attempts to remove some parts of original test case then checks if the problem still occurs. When debugging in a [[Graphical user interface|GUI]], the programmer can try skipping some user interaction from the original problem description to check if the remaining actions are sufficient for causing the bug to occur.

Line 47 ⟶ 50:

==Techniques==

* ''Interactive debugging'' uses debugger tools which allow ana program's execution to be processed one step at a time and to be paused to inspect or alter its state. Subroutines or function calls may typically be executed at full speed and paused again upon return to their caller, or themselves single stepped, or any mixture of these options. Setpoints may be installed which permit full speed execution of code that is not suspected to be faulty, and then stop at a point that is. Putting a setpoint immediately after the end of a program loop is a convenient way to evaluate repeating code. Watchpoints are commonly available, where execution can proceed until a particular variable changes, and catchpoints which cause the debugger to stop for certain kinds of program events, such as exceptions or the loading of a shared library.

* ''{{visible anchor|Print debugging}}'' or ''[[Tracing (software)|tracing]]'' is the act of watching (live or recorded) trace statements, or print statements, that indicate the flow of execution of a process and the data progression. Tracing can be done with specialized tools (like with GDB's trace) or by insertion of trace statements into the source code. The latter is sometimes called ''{{visible anchor|printf debugging}}'', due to the use of the [[printf]] function in C. This kind of debugging was turned on by the command TRON in the original versions of the novice-oriented [[BASIC]] programming language. TRON stood for, "Trace On." TRON caused the line numbers of each BASIC command line to print as the program ran.

* ''Activity tracing'' is like tracing (above), but rather than following program execution one instruction or function at a time, follows program activity based on the overall amount of time spent by the processor/CPU executing particular segments of code. This is typically presented as a fraction of the program's execution time spent processing instructions within defined memory addresses (machine code programs) or certain program modules (high level language or compiled programs). If the program being debugged is shown to be spending an inordinate fraction of its execution time within traced areas, this could indicate misallocation of processor time caused by faulty program logic, or at least inefficient allocation of processor time that could benefit from optimization efforts.

* ''{{visible anchor|Remote debugging}}'' is the process of debugging a program running on a system different from the debugger. To start remote debugging, a debugger connects to a remote system over a communications link such as a local area network. The debugger can then control the execution of the program on the remote system and retrieve information about its state.

* ''Post-mortem debugging'' is debugging of the program after it has already [[crash (computing)|crashed]]. Related techniques often include various tracing techniques like examining log files, outputting a [[call stack]] on the crash,<ref>{{cite web|url=https://www.drdobbs.com/tools/postmortem-debugging/185300443|title=Postmortem Debugging|work=Dr. Dobb's |access-date=2019-12-17|archive-date=2019-12-17|archive-url=https://web.archive.org/web/20191217045909/https://www.drdobbs.com/tools/postmortem-debugging/185300443|url-status=live}}</ref> and analysis of [[memory dump]] (or [[core dump]]) of the crashed process. The dump of the process could be obtained automatically by the system (for example, when the process has terminated due to an unhandled exception), or by a programmer-inserted instruction, or manually by the interactive user.

* ''"Wolf fence" algorithm:'' Edward Gauss described this simple but very useful and now famous algorithm in a 1982 article for [[Communications of the ACM]] as follows: "There's one wolf in Alaska; how do you find it? First build a fence down the middle of the state, wait for the wolf to howl, determine which side of the fence it is on. Repeat process on that side only, until you get to the point where you can see the wolf."<ref>{{cite journal |url=https://dl.acm.org/citation.cfm?id=358690.358695 |title=Pracniques: The 'Wolf Fence' Algorithm for Debugging |author=E. J. Gauss |journal=Communications of the ACM |year=1982 |volume=25 |issue=11 |page=780 |doi=10.1145/358690.358695|s2cid=672811 |doi-access=free }}</ref> This is implemented e.g. in the [[Git (software)|Git]] [[version control system]] as the command ''git bisect'', which uses the above algorithm to determine which [[commit (data management)|commit]] introduced a particular bug.

* ''[[Record and replay debugging]]'' is the technique of creating a program execution recording (e.g. using Mozilla's free [[rr (debugging)|rr]] debugging tool; enabling reversible debugging/execution), which can be replayed and interactively debugged. Useful for remote debugging and debugging intermittent, non-deterministic, and other hard-to-reproduce defects.

* ''[[Time travel debugging]]'' is the process of stepping back in time through source code (e.g. using [[Undo (company)|Undo LiveRecorder]]) to understand what is happening during execution of a computer program; to allow users to interact with the program; to change the history if desired and to watch how the program responds.

* ''[[Delta Debuggingdebugging]]''{{snd}} a technique of automating test case simplification.<ref>{{cite book |last=Zeller |first=Andreas |date=2005 |title=Why Programs Fail: A Guide to Systematic Debugging |publisher=Morgan Kaufmann |isbn=1-55860-866-4}}</ref>{{rp|p.123}}<!-- for redirect from 'Saff Squeeze' -->

* ''Saff Squeeze''{{snd}} a technique of isolating failure within the test using progressive inlining of parts of the failing test.<ref>{{cite web|url=http://www.threeriversinstitute.org/HitEmHighHitEmLow.html|archive-url=https://web.archive.org/web/20120311131729/http://www.threeriversinstitute.org/HitEmHighHitEmLow.html|url-status=dead|archive-date=2012-03-11|title=Kent Beck, Hit 'em High, Hit 'em Low: Regression Testing and the Saff Squeeze}}</ref><ref>{{cite web |last1=Rainsberger |first1=J.B. |title=The Saff Squeeze |url=https://blog.thecodewhisperer.com/permalink/the-saff-squeeze |website=The Code Whisperer |date=28 March 2022 |access-date=28 March 2022}}</ref>

* ''Causality tracking'': There are techniques to track the cause effect chains in the computation.<ref>{{cite journal|last=Zeller|first=Andreas|date=2002-11-01|title=Isolating cause-effect chains from computer programs|journal=ACM SIGSOFT Software Engineering Notes|volume=27|issue=6|pages=1–10|doi=10.1145/605466.605468|s2cid=12098165|issn=0163-5948}}</ref> Those techniques can be tailored for specific bugs, such as null pointer dereferences.<ref name="BondNethercote2007">{{cite book |last1=Bond|first1=Michael D.|title=Proceedings of the 22nd annual ACM SIGPLAN conference on Object oriented programming systems and applications - OOPSLA '07|last2=Nethercote|first2=Nicholas|last3=Kent|first3=Stephen W.|last4=Guyer|first4=Samuel Z.|last5=McKinley|first5=Kathryn S.|chapter=Tracking bad apples|year=2007|pages=405|doi=10.1145/1297027.1297057|isbn=9781595937865|s2cid=2832749}}</ref>

Line 113 ⟶ 116:

{{Wikibooks|Computer Programming Principles|Maintaining/Debugging|Debugging}}

* [http://www.dumpanalysis.org/ Crash dump analysis patterns]{{snd}} in-depth articles on analyzing and finding bugs in crash dumps

* [https://webwww.archive.org/web/20070218145734/http://www-128cs.ibmusfca.comedu/developerworks~parrt/webdoc/library/wa-debugdebugging.html?ca=dgr-lnxw03Dbug LearnThe the essentialsEssentials of debuggingDebugging]{{snd}} how to improve your debugging skills, a good article at [[IBM]] developerWorks (archived from the original on February 18, 2007)

* [http://www.clarinox.com/docs/whitepapers/EmbeddedDebugger.pdf Plug-in Based Debugging For Embedded Systems]

* [https://web.archive.org/web/20120112200659/http://www.byteparadigm.com/embedded-systems-test-and-debug---about-digital-input-generation-135.html Embedded Systems test and debug – about digital input generation]{{snd}} results of a survey about embedded system test and debug, Byte Paradigm (archived from the original on January 12, 2012)