2023年全國碩士研究生考試考研英語一試題真題（含答案詳解+作文范文）_第1頁
已閱讀1頁，還剩6頁未讀， 繼續(xù)免費閱讀

下載本文檔

版權(quán)說明：本文檔由用戶提供并上傳，收益歸屬內(nèi)容提供方，若內(nèi)容存在侵權(quán)，請進行舉報或認(rèn)領(lǐng)

文檔簡介

1、TheELFObjectFileFmat:IntroductionApr011995ByEricYoungdaleTheExecutableLinkingFmat(ELF)hasbeenapopulartopiclately.PeoplewonderwhythekernelconfigurationsaskswhethernottoconfigureloadingELFexecutables.AsELFwilleventuallybet

2、hecommonobjectfilefmatfLinuxbinariesitisappropriatetodocumentitabit.ThismonthEricintroducesustoELFnextmonthhewillgiveusaguidedtourofrealELFfiles.NowthatweareonthevergeofapublicreleaseofELFfilefmatcompilersutilitiesitisal

3、ogicaltimetoexplainthedifferencesbetweena.outELFdiscusshowtheywillbevisibletotheuser.AslongasIamatitIwillalsoguideyouonatouroftheinternalsoftheELFfilefmatshowyouhowitwks.IrealizethatLinuxusersrangefrompeoplebrnewtoUnixto

4、peoplewhohaveusedUnixsystemsfyears—fthisreasonIwillstartwithafairlybasicexplanationwhichmaybeoflittleusetothemeexperiencedusersbecauseIwouldlikethisarticletobeusefulinsomewaytoasmanypeopleaspossible.Peopleoftenaskwhywear

5、ebotheringwithanewfilefmat.Acouplereasonscometomind—firstthecurrentsharedlibrariescanbesomewhatcumbersometobuildespeciallyflargepackagessuchastheXWindowSystemthatspanmultipledirecties.Secondthecurrenta.outsharedlibrarysc

6、hemedoesnotsupptthedlopen()functionwhichallowsyoutotellthedynamicloadertoloadadditionalsharedlibraries.WhyELFTheUnixcommunityseemstobestardizingthisfilefmatvariousimplementationsofSVr4suchasMIPSSolarisUnixwarecurrentlyus

7、eELFSCOwillreptedlyswitchtoELFinthenearfuturetherearerumsofothervendsswitchingtoELF.Oneinterestingsidenote—WindowsNTusesafilefmatbasedupontheCOFFfilefmattheSVr3filefmatthattheUnixcommunityisaboninginfavofELF.Letusstartat

8、thebeginning.UserswillgenerallyencounterthreetypesofELFfiles—.ofilesregularexecutablessharedlibraries.Whileallofthesefilesservedifferentpurposestheirinternalstructurefilesarequitesimilar.Thuswecanbeginwithageneraldeionpr

9、oceedtoadiscussionofthespecificsofthethreefiletypes.NextmonthIwilldemonstratetheuseofthereadelfprogramwhichcanbeusedtodisplayinterpretvariousptionsofELFfiles.OneuniversalconceptamongalldifferentELFfiletypes(alsoa.outmany

10、otherexecutablefilefmats)isthenotionofasection.Thisconceptisimptantenoughtospendsometimeexplaining.Simplyputasectionisacollectionofinfmationofasimilartype.Eachsectionrepresentsaptionofthefile.Fexampleexecutablecodeisalwa

11、ysplacedinasectionknownas.textalldataofallofthesymbols(programentrypointsaddressesofvariablesetc.)thataredefinedreferencedwithinthefiletheaddressassociatedwiththesymbolsomekindoftagindicatingthetypeofthesymbol.Inana.outf

12、ilethisismelesstheextentoftheinfmationpresentasweshallseelaterELFfileshaveconsiderablymeinfmation.Insomecasesthesymboltablescanberemovedwiththestriputility.Theadvantageisthattheexecutableissmalleroncestrippedbutyouloseth

13、eabilitytodebugthestrippedbinary.Witha.outitisalwayspossibletoremovethesymboltablefromafilebutwithELFyoutypicallyneedsomesymbolicinfmationinthefileftheprogramtoloadrun.ThusinthecaseofELFthestripprogramwillremoveaptionoft

14、hesymboltablebutitwillneverremoveallofthesymboltable.(.dynsym)Finallyweneedtodiscusstheconceptofrelocations.Letussayyoucompileasimple“hellowld”program:main()printf(“HelloWldn”)Thecompilergeneratesanobjectfilewhichcontain

15、sareferencetothefunctionprintf.Sincewehavenotdefinedthissymbolitisanexternalreference.Theexecutablecodefthisfunctionwillcontainaninstructiontocallprintfbutintheobjectcodewedonotyetknowtheactuallocationtocalltoperfmthisfu

16、nction.Theassemblernoticesthatthefunctionprintfisexternalitgeneratesarelocationwhichcontainsseveralcomponents.Firstitcontainsanindexintothesymboltable—thiswayweknowwhichsymbolisbeingreferenced.Seconditcontainsanoffsetint

17、othe.textsectionwhichreferstotheaddressoftheoperofthecallinstructions.Finallyitcontainsatagwhichindicateswhattypeofrelocationisactuallypresent.Whenyoulinkthisfilethelinkerwalksthroughtherelocationslooksupthefinaladdresso

18、ftheexternalfunctionprintfthenpatchesthisaddressbackintotheoperofthecallinstructionsothecallinstructionnowpointstotheactualfunctionprint.a.outexecutableshavenorelocations.Thekernelloadercannotresolveanysymbolswillrejecta

19、nyattempttorunsuchabinary.Ana.outobjectfilewillofcoursehaverelocationsbutthelinkermustbeabletofullyresolvethesetogenerateausableexecutable.SofareverythingIhavedescribedappliestobotha.outELF.NowIwillenumeratetheshtcomings

溫馨提示

  • 1. 本站所有資源如無特殊說明，都需要本地電腦安裝OFFICE2007和PDF閱讀器。圖紙軟件為CAD,CAXA,PROE,UG,SolidWorks等.壓縮文件請下載最新的WinRAR軟件解壓。
  • 2. 本站的文檔不包含任何第三方提供的附件圖紙等，如果需要附件，請聯(lián)系上傳者。文件的所有權(quán)益歸上傳用戶所有。
  • 3. 本站RAR壓縮包中若帶圖紙，網(wǎng)頁內(nèi)容里面會有圖紙預(yù)覽，若沒有圖紙預(yù)覽就沒有圖紙。
  • 4. 未經(jīng)權(quán)益所有人同意不得將文件中的內(nèi)容挪作商業(yè)或盈利用途。
  • 5. 眾賞文庫僅提供信息存儲空間，僅對用戶上傳內(nèi)容的表現(xiàn)方式做保護處理，對用戶上傳分享的文檔內(nèi)容本身不做任何修改或編輯，并不能對任何下載內(nèi)容負(fù)責(zé)。
  • 6. 下載文件中如有侵權(quán)或不適當(dāng)內(nèi)容，請與我們聯(lián)系，我們立即糾正。
  • 7. 本站不保證下載資源的準(zhǔn)確性、安全性和完整性, 同時也不承擔(dān)用戶因使用這些下載資源對自己和他人造成任何形式的傷害或損失。

評論

0/150

提交評論