华南理工大学汇编原理课件06.ppt

Chapter6 Procedure过程 Textbook 7ProgramLogicandControl Outline StackPUSHPOPProcedureDirectivesCALLRETSubprogramprogrammingMethodsofpassingparameters 8086Stack8086堆栈 6 1 Stack 堆栈 Stackcontainsanydataandaddressesthattheprogramneedstosavetemporarilyorforusebyyourown called subroutines Thestacksegment SS registeraddressesthestacksegment 堆栈是供程序使用的连续的内存空间 用于保存一些临时数据 MainUse Theprogramcallsasubroutineforspecialprocessing Itsavesthereturnaddressinthestack whichthesubroutinelaterusesforreturning Theprogramthatcallsthesubroutinemayalsopassdatabyplacingitinthestack wherethesubroutineaccessesit Theprogramhastoperformcalculationsthatusetheregisters itcansavethepresentcontentsoftheregistersonthestack makethecalculations andthenrestorethedatafromthestacktotheregisters Stack 堆栈 Thestackdiffersfromothersegmentsinitsmethodofstoringdata Itbeginsstoringdataatthehighestlocationinthesegmentandstoresdatadownward orbackward throughmemory LastinFirstOut是一种具有特殊访问方式的存储空间 特殊性在于 最后进入这个空间的数据 最先出去 PUSH POP Stack Initially thestackisemptyanditlookslikethis Examples movbx 2266Hpushbxmovcx 1122Hpushcxpopaxpopbx PAStackFrame OperationofPUSHBX 1 Initially thestackisemptyanditlookslikethis SS SP 1000 000E Examples SS 1000HSP 000EHbx 2266H PAStackFramePointer OperationofPUSHBX 2 1 DecrementSPby2 000C SP SP 2SS SP 1000 000C Examples PAStackFramePointer OperationofPUSHBX 3 2 StorethecontentsofBX 2266 inthestack Notethesequenceofthestoredbytes Examples SS 1000HSP 000CH storesdatadownward orbackward throughmemory 入栈时 栈顶从高地址向低地址方向增长 stack DecrementsSPby2 000Ah andstoresthecontentsofCXinthestack After state Examples movcx 1122Hpushcx stack RestoresthewordfromwhereSPpointsinthestack 000AH toAXandincrementsSPby2 000CH After state ax 1122H Examples popax PAStackFramePointer stack RestoresthewordfromwhereSPpointsinthestack 000CH toBXandincrementsSPby2 000EH After state bx 2266H Examples popbx PAStackFramePointer OperationofPOPBX 1 Initialstate SS SP1000 000C Examples SS 1000HSP 000CH PAStackFramePointer OperationofPOPBX 2 1 RestoresthewordfromwhereSPpointsinthestack 000CH toBX SS SP1000 000C Examples SS 1000HSP 000CHbx 2266H PAStackFramePointer OperationofPOPBX 3 2 AndincrementsSPby2 000EH SP SP 2SS SP1000 000EBX 2266H Examples PAStackFramePointer OperationofPOPBX 3 Note thePOPinstructionsarecodedinreversesequencefromPUSHinstructions 入栈时 栈顶从高地址向低地址方向增长 Examples PAStackFramePointer Stack 堆栈 Stackcontainsanydataandaddressesthattheprogramneedstosavetemporarily Thestacksegment SS registeraddressesthestacksegment 堆栈是供程序使用的连续的内存空间 用于保存一些临时数据 Instructions PUSH POP PUSH DecrementsSPby2andstoresthecontentsofthesourceoperandinthestack POP RestoresthewordfromwhereSPpointsinthestacktothedestinationoperandandincrementsSPby2 PUSHSRC pushontothestack SRCcanber16 m16 seg reg imm SP SP 2 SS SP r16 m16 seg Operations SP SP 2 SP SCR SP 1 SCR 1 notaffectflag PUSHInstruction POPInstruction Operations DST SP DST 1 SP 1 SP SP 2 POPDes Descanber16 m16 seg reg exceptcs r16 m16 seg SS SP SP SP 2 2 出栈指令POP 现场保护恢复 pushax whenenterasubroutinepushbxpushdx popdx whenexitfromthesubroutinepopbxpopax Examples Note 1 AllowPUSHimm notallowPOPimm 2 AllowPUSHCS notallowPOPCS 3 PUSHinstructionpushesawordontostackanddecrementthespby2 8086or80286 PUSHinstructionpushes2wordsontostackanddecrementthespby4 80386orlater PUSH Summary 1 Stackisalocationspaceinstack segment workaccordingtoFirst in last out 2 Justoneentry exit soonlyoneSP ThecontentofSPpointtothecurrenttop inoroutlocation ofthestackatanytime 3 PUSHorPOPaword notallowbyte 4 Anyaddressing exceptimmediate addressing 5 PUSHandPOPinstructionnotaffectflag bit ProcedureBody CallandReturn过程体 调用和返回 6 2 Procedure AprocedureisablockofcodethatbeginswiththePROCdirectiveandterminateswithENDPdirective Procedure Organizingaprogramintoproceduresprovidessomebenefits 1 Reducestheamountofcodebecauseacommonprocedurecanbecalledfromanynumberofplacesinthecodesegment 2 Encouragesbetterprogramorganization Procedure 3 Facilitatesdebuggingofaprogrambecausedefectscanbemoreclearlyisolated 4 Helpsintheongoingmaintenanceofprogramsbecauseproceduresarereadilyidentifiedformodification Outline ProcedureDirectiveInstructionsCALLRETSubroutineProgramming ProcedureDirectives AcodesegmentcontainsoneormoreproceduresOneprocedurecodedas ProcNamePROC near far entrypointforfirstinstructiontoexecute endaprocedureProcNameENDP ProcedureDirectives Theprocedurename ProcName mustbepresent uniqueandfollowassemblernamingconventions TheprocedureattributecanisNEAR FAR defaultisNEAR thatis within 32K attribute ProcNamePROC near far ProcNameENDP Callingprocedureandprocedure Instructions Format label2 RET pop value label1 CALLproc name Instructions Callinstructionistotransfercontroltoacalledprocedure RETinstructionreturnsfromthecalledproceduretotheoriginalcallingprocedure theinstructionafterCALLinstruction RETshouldbethelastinstructioninthecalledprocedure NearCallandReturn Acalltoaprocedurewithinthesamesegmentisnear Performs 1 bymeansofapushoperation decrementsSPby2 oneword andtransfersIPvalueontothestack 2 insertstheoffsetaddressofthecalledprocedureintoIP NearCallandReturn ARETthatreturnsfromanearprocedurebasicallyreversestheCALLsteps 1 popstheoldIPvaluefromthestackbackintoIP 2 incrementsSPby2 FarCallandReturn Afarcallcallsaprocedurelabeledfar possiblyinanothercodesegment Performs 1 firstpushesthecontentsofCSontothestackandinsertsthenewsegmentaddressinCS 2 thenpushesIPontothestackandinsertsanewoffsetaddressinIP FarCallandReturn TheCS IPpairnowpointstotheaddressofthefirstinstructiontoexecuteinthecalledsubprogram FarCallandReturn Onexitfromthecalledprocedure AfarRETreversestheCALLsteps popsboththeoriginalIPandCSaddressesbackintotheirrespectiveregisters FarCallandReturn TheCS IPpairnowpointstotheaddressoftheinstructionfollowingtheoriginalCALL CALLInstruction Fourtypes JMP CALLlabel Intra segmentdirect段内直接CALLr16 m16 Inter segmentdirect段内间接CALLfarptrlabel Inter segmentdirect段间直接CALLfarptrmem Inter segmentIndirect段间间接 CALLInstruction TheassemblercantellfromtheprocedurewhetherRETisnearorfarandgeneratestheappropriateobjectcode Butyoucanuse nearptr or farptr tosettheattribute CALLInstruction FourtypesofCALL CALLlabel 段内调用 相对寻址 SP SP 2 SS SP IP IP IP 16位位移量CALLr16 m16 段内调用 间接寻址 SP SP 2 SS SP IP IP r16 m16 label theprocedurename Nearcallandreturn Nearcall program beforecall memory stack Figure8 EffectonthestackandIPbyNearcall 0FFF 00031002 CALLInstruction FourtypesofCALL CALLfarptrlabel 段间调用 直接寻址 SP SP 2 SS SP CS SP SP 2 SS SP IP IP label偏移地址 CS label段地址 子程序调用指令 FourtypesofCALLNotethearrangementofthememory CALLfarptrmem 段间调用 间接寻址 SP SP 2 SS SP CS SP SP 2 SS SP IP IP mem CS mem 2 RETInstruction RETinstructionreturnsfromthecalledproceduretotheoriginalcallingprocedure theinstructionafterCALLinstruction Format RET CallingProcedureandCalledProcedure Subprogramprogramming Aprogrammingconventionistoprovidecommentsatthestartofeachproceduretoidentifyitspurposeandregistersused And ifnecessary topushchangedregistersatthestartandtopopthemonexiting subprogram subnameprocpushaxpushbxpushcx procedurebodypopcx note inreverseorderpopbxpopaxretsubnameendp Examples ifnecessary topushchangedregistersatthestartandtopopthemonexiting DisplayCR carriagereturn LF linefeed Examples Examples DisplayCR LF result ParametersandLocalVariable参数和局部变量 6 3 PassingParameters Passingparametersbyvalue theactualdataitem PassvaluesinregistersPassvaluesinstackPassingparametersbyreference theaddressofthedata AddressesinregistersAddressesinstack 例4 11求校验和 子程序计算数组元素的 校验和 校验和是指不记进位的累加入口参数 数组的逻辑地址 传址 元素个数 传值 出口参数 求和结果 传值 Passingparametersinregister 入口参数 cx 元素个数 DS BX 数组的段地址 偏移地址出口参数 al 校验和 Examples Passingparametersinregisters Examples Passingparametersinregisters Passingparametersinvariables 入口参数 count 元素个数 array 数组名 含段地址 偏移地址 出口参数 result 校验和 Examples Passingparametersinvariables Recursion递归 6 4 recursive Arecursi