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(qǐng)進(jìn)行舉報(bào)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(qǐng)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(qǐng)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(huì)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(chǔ)空間，僅對(duì)用戶上傳內(nèi)容的表現(xiàn)方式做保護(hù)處理，對(duì)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(duì)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(qǐng)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(shí)也不承擔(dān)用戶因使用這些下載資源對(duì)自己和他人造成任何形式的傷害或損失。
最新文檔
- the_elf_object_file_format_by_dissection
- format2012
- Exterior cad Format.dwg
- file.txt
- File.pdf
- file.txt
- file.txt
- file.txt
- Exterior cad Format.dwg
- inspiration of gestalt psychology to the format design
- Exterior cad Format.dwg
- file.gif
- Exterior cad Format.dwg
- general guidelines for cover letter format
- 銷流程_final_format
- file.txt
- file.txt
- file.txt
- file.txt
- File (1).pdf
評(píng)論
0/150
提交評(píng)論