Evil has planted a slew of binary bombs on our machines A binary bomb is a program that consists of a sequence of phases Each phase expects you to type a particular string on the standard input stdin If you type the correct string then the phase i ID: 74901
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Step2:DefuseYourBombYourjobistodefusethebomb.Youcanusemanytoolstohelpyouwiththis;pleaselookatthehintssectionforsometipsandideas.Thebestwayistousethegdbdebuggertostepthroughthedisassembledbinary.Eachtimeyourbombexplodesitnotiesthestaff,andyoulose1/4point(uptoamaxof10points)inthenalscoreforthelab.Sothereareconsequencestoexplodingthebomb.Youmustbecareful!Inamomentofweaknesshowever,Dr.Evildecidedthattherst10bombexplosionswillbefreeofcharge.Eachphaseisworth10points,foratotalof60points.Thephasesgetprogressivelyhardertodefuse,buttheexpertiseyougainasyoumovefromphasetophaseshouldoffsetthisdifculty.Thebombignoresblankinputlines.Ifyourunyourbombwithacommandlineargument,forexample,bash$./bombbsol.txtthenitwillreadtheinputlinesfrombsol.txtuntilitreachesEOF(endofle),andthenswitchovertothestandardinput(stdin).Thisway,youdon'thavetokeepretypingthesolutionstophasesyouhavealreadydefused.Toavoidaccidentlydetonatingthebomb,youwillneedtolearnhowtosingle-stepthroughtheassemblycodeandhowtosetbreakpoints.Youwillalsoneedtolearnhowtoinspectboththeregistersandthememorystates.Oneoftheniceside-effectsofdoingthelabisthatyouwillgetverygoodatusingadebugger.Thisisacrucialskillthatwillpaybigdividendstherestofyourcareer.LogisticsYoumayworkinagroupofupto2people.Youshoulddotheassignmentonfelix.csc.villanova.edu.Infact,thereisarumorthatDr.Evilreallyisevil,andthebombwillalwaysblowupifrunelsewhere.Thereareseveralothertamper-proongdevicesbuiltintothebombaswell,orsotheysay.Hand-InThereisnoexplicithand-in.Thebombwillnotifyyourinstructorautomaticallyafteryouhavesuccessfullydefusedit.Youcankeeptrackofhowyou(andtheothergroups)aredoingbylookingathttp://www.csc.villanova.edu/˜mdamian/csc2400/bomblab.htmlThiswebpageisupdatedcontinuouslytoshowtheprogressofeachgroup.2 gdb./bombkDisassembletherstphaseusingdisasphase_1Youwillseethatthisphasecallsafunctioncalledstrings not equal.2.Setabreakpointtocallstrings not equalbreak*(phase_1+???)Displaythenextmachineinstructiontobeexecutedeachtimethedebuggersuspendsexecution,soyouknowwhereyouareatalltimes:display/i$eipThenruntheprogramuptotherstbreakpoint–youwillneedtotypeinyourownstring(typeinanarbitrarystring,suchas123456)togetpastthepointwheretheprogramiswaitingforuserinput.Weallknowthat,priortothecall not �equalmachineinstruction,theargumentsforstrings not equalarepushedintothestack(inparticular,theaddressesofthetwostringsthataretobecompared).Inspectthetwowordsatthetopofthestacktolearntheseaddresses:x/2xw$espNextinspectthememorycontentsattheaddressesyou'velearned.x/saddresswhereaddressiswhatgetspushedontothestackbeforethecalltostrings not equal.Thisshouldrevealthesecretstringforyou.3.Supposethatyouarenishedwithphase 1,andarereadytostartphase 2.Afterdefusingphase 1,theprogramwillwaitforinputfromyoutobeusedinphase 2.Inthiscase,itwillwaitforsixnumbersseparatedbyspaces.Asbefore,disassemblethecodeforphase 2usingdisasphase_2Youwillseethatphase 2seeks6integersthatsatisfycertainconditions.Focusonthecmpinstruc-tionsandinspecttheargumentsbeingcompared.4