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A SIMPLE METHOD FOR GENERATING SELF-RELOCATING PROGRAMS or To every problem, no matter how trivial, someone can always find a complicated solution. The "What" ┴ self-relocatinτ prograφ is¼á iε CP/═ terminology¼ onσ whicΦ wheε loadeΣ int∩ ì thσ bottoφ oµ thσ transien⌠ prograφ areß move≤ itselµ u≡ t∩ thσ to≡ oµ thσ TP┴ ì beforσá doinτ anythinτ useful«á Thσ effec⌠ i≤ t∩ freσ u≡ thσ lowe≥ enΣ oµ thσ ì TPA for use by other programs. This is how program monitors such as DDT work. The "Why" Oεá anΣá ofµ ove≥ thσ pas⌠ yea≥ ╔ havσ beeε writinτ ß supe≥á Z8░á disassemble≥ ì whicΦá include≤ thσ morσ usefu∞ feature≤ oµ WarΣ Christensen'≤á RESOURC┼á (seσ ì CPMU╟á vo∞ 42⌐ alonτ witΦ ß fe≈ feature≤ oµ m∙ owε inventioε anΣ ß bette≥ use≥ ì interface«á I⌠á occureΣá t∩ mσ ho≈ convenien⌠ i⌠ woulΣ bσ t∩á havσá thσá dis-ì assemble≥á residσ iε higΦ memor∙ s∩ tha⌠ thσ prograφ beinτ disassembleΣá coulΣ ì occup∙ it≤ norma∞ positioε iε thσ TPA« Iε thσ documentatioε oε RESOURCE¼ WarΣ ì says: áááááááááá"..«á typicall∙á yo⌡á wan⌠ t∩ disassemblσ ß prograφá whicΦ ì áááááááááárun≤á a⌠á 100H¼á whicΦ i≤ werσ RESOURC┼á runs«á BoΓá Vaε ì ááááááááááValzaΦáá woulΣá havσá solveΣá tha⌠á b∙áá makinτáá resourcσ ì áááááááááárelocatablσá anΣá movinτ itselµ u≡ unde≥ BDOS«á ╔á wasn'⌠ ì áááááááááátha⌠ industrious." Instead¼á hσá fiddle≤ arounΣ witΦ aε "invisiblσ offsetó whicΦ make≤ ßá prograφ ì loadeΣá ABOV┼ thσ disassemble≥ looδ a≤ thougΦ i⌠ reside≤ a⌠ 100h«á Ward'≤á owε ì word≤ describσ m∙ feeling≤ oε thσ matter║ ╔ wasn'⌠ tha⌠ industriousí Thu≤ wa≤ ì ╔ leΣ t∩ conside≥ thσ method≤ oµ generatinτ self-relocatinτ programs. And the "How" Thσá enΣ resul⌠ oµ al∞ SR╨ generatioε scheme≤ i≤ aε objec⌠ prograφá comprisinτ ì threσá discretσá segments¼á normall∙ (bu⌠ no⌠ necessarily⌐á iεá thσá followinτ ì order: 1. Relocator module: ááááááááááááááá┴ shor⌠ sectioε oµ codσ whicΦ shift≤ thσ relocatablσ segmen⌠ t∩ ì áááááááááááááááthe top of the TPA and transfers control to it. 2. Relocatable program segment: áááááááááááááááThe "useful" part of the SRP. 3. Relocation bitmap: áááááááááááááááUseΣá b∙á thσá relocato≥á modulσ t∩ fi°á u≡á addresse≤á iεá thσ ì ááááááááááááááárelocatable program segment to reflect the new program origin. ┴á bi⌠ oµ sneaker∙ i≤ involveΣ iε thσ generatioε anΣ usσ oµá thσá bitmap«á I⌠ ì contain≤á onσá BI╘ fo≥ eacΦ BYT┼ oµ codσ iε thσ relocatablσá prograφá segment« ì Oncσá thσá relocatablσ codσ i≤ moveΣ int∩ placσ thσ bitma≡ i≤ scanneΣ anΣá fo≥ ì eacΦá bi⌠á set¼á ß relocatioε bia≤ i≤ addeΣ t∩ thσ correspondinτ bytσá oµá thσ ì relocateΣ code«á Thi≤ devilishl∙ simplσ schemσ relie≤ oε thσ wa∙ iε whicΦ thσ ì bitma≡á i≤á constructed«á Tw∩á codσá file≤ arσ prepareΣá sucΦá tha⌠á al∞á thσ ì addresse≤á iε onσ diffe≥ froφ thosσ iε thσ othe≥ b∙ aε exac⌠ multiplσá oµá 25╢ ì anΣ thσ bitma≡ i≤ constructeΣ sucΦ tha⌠ ß bi⌠ i≤ se⌠ iµ thσ correspondinτ codσ ì byte≤ arσ differen⌠ and¼á conversely¼ ß bi⌠ i≤ rese⌠ iµ thσ correspondinτ codσ ì bytes are the same. The following example may help to explain the idea: 0000 3A 0010 LD A,(NUMBER+1) ;Get whatever junk is in NUMBER 0003 CD 0011 CALL HEXOUT ;Display high-order byte in hex 0006 3A 000F LD A,(NUMBER) ;Get rest of NUMBER 0009 CD 0011 CALL HEXOUT ;Display low-order byte in hex 000C C3 0000 JP 0 ;End 000F NUMBER: 000F 7A49 DEFW 7A49h ;Arbitrary 16-bit thing 0011 HEXOUT: 0011 F5 PUSH AF ;Copy for displaying low-order nibble 0012 0F RRCA ;Isolate the high-order nibble 0013 0F RRCA 0014 0F RRCA 0015 0F RRCA 0016 CD 001A CALL HEXDIG ;Display a hex digit 0019 F1 POP AF ;Recover low-order bits 001A HEXDIG: 001A E6 0F AND 0Fh ;Drop spurious bits 001C C6 90 ADD A,90h ;Convert hex digit to ASCII 001E 27 DAA 001F CE 40 ADC A,40h 0021 27 DAA 0022 5F LD E,A ;Move to E for CP/M console output 0023 0E 02 LD C,2 ;Function selector 0025 C3 0005 JP 5 ;BDOS will do the RETurn for us With the code origin set at 0 the object code for the above program is: 3A 10 00 CD 11 00 3A 0F 00 CD 11 00 C3 00 00 49 7A F5 0F 0F 0F 0F CD 1A 00 F1 E6 0F C6 90 27 CE 40 27 5F 0E 02 C3 05 00 Setting the code origin at 100h would generate the following object code: 3A 10 01 CD 11 01 3A 0F 01 CD 11 01 C3 00 00 49 7A F5 0F 0F 0F 0F CD 1A 01 F1 E6 0F C6 90 27 CE 40 27 5F 0E 02 C3 05 00 The code is 40 bytes long so the bitmap would be 40 bits long, i.e. 5 bytes: 0 0 1 0 0 1 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 which, in hex notation is 24 90 00 80 00. è Supposσá wσ no≈ loaΣ thσ origin-░ codσ a⌠ A60░ t∩ A627«á Thσ bitma≡ tell≤á u≤ ì tha⌠ wσ havσ t∩ adΣ A6Φ t∩ thσ codσ byte≤ a⌠ A602¼á A605¼ A608¼ A60┬ anΣ A618« ì The properly-relocated code becomes: 3A 10 A6 CD 11 A6 3A 0F A6 CD 11 A6 C3 00 00 49 7A F5 0F 0F 0F 0F CD 1A A6 F1 E6 0F C6 90 27 CE 40 27 5F 0E 02 C3 05 00 So what's hard about that? Nothing¼á onσ woulΣ think«á Unfortunately¼ thσ commonl∙ availablσ method≤ fo≥ ì buildinτá bitmap≤ anΣ constructinτ self-relocatablσ program≤ arσ s∩ mess∙ tha⌠ ì ╔á coulΣ almos⌠ sympathisσ witΦ WarΣ Christensen'≤ vie≈ oµá thσá exercise«á ╔ ì shal∞á describσá onσ sucΦ methoΣ anΣ briefl∙ mentioε tw∩ other≤ bu⌠á witΦá thσ ì forewarninτá tha⌠ ╔ havσ neve≥ an∙ oµ theφ anΣ tha⌠ ╔ aφ relyinτ oε sucΦ scan⌠ ì documentatioεá a≤ ╔ havσ availablσ anΣ oε wha⌠ ╔ coulΣ learε b∙á halfheartedl∙ ì playinτá arounΣá witΦ them«á Halfheartedly┐á Yes¼á afte≥ al∞ i⌠á wa≤á fairl∙ ì obviou≤ tha⌠ ╔ woulΣ neve≥ seriousl∙ emplo∙ eithe≥ methoΣ anΣ m∙ onl∙ interes⌠ ì iε theφ wa≤ attemptinτ t∩ removσ thσ wildes⌠ inaccuracie≤ froφ thesσ notes. The GENMOD method Normall∙á distributeΣ witΦ MP/═ bu⌠ sometime≤ availablσ witΦ CP/═ i≤ ß utilit∙ ì prograφá calleΣ GENMOD«á Thσ step≤ iε thσ GENMO─ techniquσ fo≥ generatinτá aε ì SRP are something like this: 1 Assemblσ thσ relocatablσ codσ segmen⌠ iε thσ norma∞ wa∙ specifyinτ ß ì áááááááááácode origin of 100h and generating a .HEX file. 2 Modify the source program changing the code origin to 0. 3á Re-assemblσá thσá relocatablσ codσ segmen⌠ int∩ ßá (different⌐á .HE╪ ì ááááááááááoutput file. 4 Concatenatσá thσ tw∩ .HE╪ files«á PI╨ ma∙ bσ useΣ t∩ d∩ thi≤ fairl∙ ì ááááááááááneatly, e.g. B>PIP RP.HEX=ORG000.HEX,ORG100.HEX 5 Ruε GENMO─ agains⌠ thσ concatenateΣ .HE╪ file, e.g.: B>GENMOD RP.HEX RP.COM GENMOD responds with: REL MOD END 002A REL MOD SIZE 007F ABS MOD END 097F GENMO─á put≤á thσ relocatablσ codσ segmen⌠ a⌠ 200Φ followeΣá b∙á tw∩ ì áááááááááábyte≤á whosσ purposσ ╔ canno⌠ fathom«á Immediatel∙ thereafte≥á come≤ ì ááááááááááthσá bitmap«á Thσ importan⌠ piecσ oµ informatioε abovσ i≤ thσá "RE╠ ì ááááááááááMO─ ENDó address«á AdΣ 200Φ t∩ tha⌠ valuσ anΣ yo⌡ havσ thσá addres≤ ì ááááááááááof the start of the bitmap. è 6 áUsσá DDT¼á ZSI─á o≥ whateve≥ t∩ loaΣ thσ relocato≥ modulσ belo≈á thσ ì áááááááááárelocatablσá codσá segmen⌠ anΣ bitmap«á Someho≈ tel∞ you≥á relocato≥ ì áááááááááámodulσá thσ lengtΦ oµ you≥ relocatablσ codσ segmen⌠ and/o≥ wherσá t∩ ì ááááááááááfinΣá thσá bitmap«á Exi⌠ froφ thσ debugge≥ anΣ SAV┼á thσá SR╨á codσ ì ááááááááááimage. B>ZSID RP.COM IRELOC.COM R {set up relocator information} G0 B>SAVE nn RP.COM and there you have it! The REL.UTL method Anothe≥ methoΣ fo≥ generatinτ SRP≤ i≤ offereΣ b∙ Rober⌠ vaε ValzaΦ (CPMU╟á vo∞ ì 38⌐ wh∩ provide≤ ß .UT╠ prograφ whicΦ run≤ unde≥ thσ contro∞ oµ SI─ o≥ ZSI─ t∩ ì handlσá somσá oµ thσ step≤ describeΣ above«á Whilσ differen⌠ iεá detail¼á thσ ì methoΣá i≤ oµ thσ samσ degreσ oµ complexit∙ a≤ thσ GENMO─átechiquσ. The macro method Usinτá ß fairl∙ powerfu∞ macr∩ assemble≥ sucΦ a≤ Digita∞ Research'≤ MA├ i⌠á i≤ ì possiblσ t∩ definσ macro≤ t∩ generatσ ß bitmap«á ┴ finσ examplσ oµ thσ usσ oµ ì this technique is provided by Gary Novosielski's UNSPOOL program. ; GENERATE A LABEL OF THE FORM ??RNN TO TAG AN ; ADDRESS REQUIRING RELOCATION: RTAG MACRO LBL,VAL ??R&LBL EQU VAL ENDM ; ; FLAG <INST> AS A RELOCATABLE INSTRUCTION ; <INST> IS OF THE FORM: <MNE OP1[,OP2]> R MACRO INST @RLBL SET @RLBL+1 RTAG %@RLBL,%2+$-@BASE INST-@BASE ENDM ; ; DURING BIT MAP CONSTRUCTION, GET THE NEXT R-TAGGED ; ADDRESS VALUE: NXTRLD MACRO NN @RLD SET ??R&NN @NXTRLD SET @NXTRLD + 1 ENDM In the code to be relocated we see these macros applied to instructions: @BASE: ;START OF CODE TO BE RELOCATED . . . R <JZ SYSREQ> 0038+= ??R2 EQU 56 0336+CA9801 JZ SYSREQ-@BASE Ever∙ instructioε whicΦ wil∞ neeΣ t∩ bσ modifieΣ durinτ relocatioε i≤ codeΣ a≤ ì ßá paramete≥á t∩ thσ "Ró macr∩ whicΦ generate≤ aε assembly-timσá symbo∞á whosσ ì valuσá i≤á thσ offse⌠ froφ thσ beginninτ oµ thσ relocatablσ codσ oµ thσá thirΣ ì instructioεá byte«á A⌠á thσ samσ timσ thσ operanΣ i≤ modifieΣá t∩á ßá simila≥ ì offset«á A⌠á thσá enΣá oµ thσ relocatablσ codσ i≤á thσá assembly-timσá bitma≡ ì generator: ; BUILD THE RELOCATION INFORMATION INTO A ; BIT MAP FOLLOWING THE CODE. ; 0000 # @X SET 0 0000 # @BITCNT SET 0 0002 # @RLD SET ??R1 0002 # @NXTRLD SET 2 RTAG %@RLBL+1,0FFFFH ;DEFINE ONE MORE SYMBOL FFFF+= ??R89 EQU 0FFFFH ; REPT SEGLEN+8 IF @BITCNT>@RLD NXTRLD %@NXTRLD ;;NEXT VALUE ENDIF IF @BITCNT=@RLD @X SET @X OR 1 ;;SET LOW BIT ENDIF @BITCNT SET @BITCNT + 1 IF @BITCNT MOD 8 = 0 DB @X ;;DEFINE THE BYTE @X SET 0 ;;CLEAR HOLD VARIABLE FOR MORE ELSE @X SET @X SHL 1 ;;NOT 8 YET. MOVE OVER. ENDIF ENDM Thσá outpu⌠á oµá thi≤ in-linσ macr∩ i≤ ß serie≤á oµá "DBóá pseudo-instruction≤ ì defining the bitmap. A≤ coded¼á thi≤ techniquσ wil∞ NO╘ worδ fo≥ an∙ oµ thσ Z8░ instruction≤á whicΦ ì havσá 16-bi⌠á opcode≤ bu⌠ ß simplσ rearrangemen⌠ oµ thσ "Ró macr∩ woulΣá solvσ ì thi≤ problem: R MACRO INST @RLBL SET @RLBL+1 INST-@BASE RTAG %@RLBL,$-%1-@BASE ENDM è Thσá macr∩ techiquσ i≤ probabl∙ thσ easies⌠ oµ thσ threσ t∩ usσ provideΣá tha⌠ ì onσá ha≤ acces≤ t∩ ß gooΣ macr∩ assembler«á ╔ usσ Microsoft'≤ MACRO-8░á (M80⌐ ì fo≥á al∞á oµ m∙ assembly-languagσ programminτ anΣ (withou⌠ puttinτ i⌠á t∩á thσ ì test⌐á ╔ doub⌠ tha⌠ M8░ coulΣ handlσ thσ task«á Nevertheles≤ thσ techniquσ i≤ ì viable¼á elegan⌠á anΣ cleve≥ althougΦ thσ complexit∙ oµ thσ macro≤á make≤á thσ ì actua∞á assembl∙á ver∙ lonτ anΣ ╔ suspec⌠ tha⌠ witΦ ß largσ prograφ onσá coulΣ ì ruεá int∩á memory-spacσá problem≤á becausσ oµá thσá largσá numbe≥á oµá symbol≤ ì generated«á Eveε iµ ╔ haΣ MA├ ╔ woulΣ no⌠ usσ thi≤ techniquσ becausσ ╔ d∩ al∞ ì oµá m∙á assembly-languagσá programminτá iε Ziloτá mnemonics«á Thesσá arσá no⌠ ì supporteΣ b∙ MAC«á Also¼á wheε ╔ firs⌠ wrotσ thi≤ articlσ ╔ wa≤ no⌠ awarσá oµ ì an∙á implementatioε oµ thσ macr∩ techniquσ anΣ ╔ doub⌠ tha⌠ ╔ woulΣ havσá beeε ì smart enough to devise those very sophisticated macros. There has to be a Better Way A⌠á thσá timσá oµá writinτá thi≤ articlσ ╔ havσá codeΣá anΣá testeΣá thσá maiε ì disassembl∙ routinσ anΣ thσ symbo∞ tablσ handlinτ routine≤ fo≥ m∙ disassemble≥ ì anΣ ╔ havσ severa∞ othe≥ pre-coded¼ testeΣ module≤ kickinτ arounΣ iε librarie≤ ì read∙á t∩ bσ incorporateΣ int∩ thσ program«á Nevertheles≤ ╔ expec⌠ tha⌠ some- ì wherσá betweeε 2░ anΣ 4╡ assembly/testinτ cycle≤ wil∞ bσ requireΣ t∩á completσ ì thσá projec⌠á anΣ thσ though⌠ oµ goinτ througΦ thσ abovσ procedurσá morσá thaε ì oncσ o≥ twicσ woulΣ bσ sufficien⌠ t∩ discouragσ mσ froφ eve≥ finishinτ it. Wha⌠ ╔ wanteΣ wa≤ aε automatiπ methoΣ oµ generatinτ aε SRP« Ideally¼ ╔ shoulΣ ì bσ ablσ t∩ d∩ somσ oµ thσ assembly/testinτ cycle≤ witΦ thσ prograφ runninτá iε ì thσ low-memor∙ enΣ oµ thσ TP┴ anΣ theε withou⌠ changinτ thσ program¼á generatσ ì aε SR╨ forφ witΦ somσ assurancσ tha⌠ i⌠ wil∞ stil∞ work« The Better Way Thσá onσá essentia∞á too∞á fo≥ thσ SR╨ generatioε schemσ tha⌠ ╔á aφá abou⌠á t∩ ì describσá i≤á aεá assembler-linke≥ combinatioε whicΦá let≤á yo⌡á specif∙á loaΣ ì addresse≤ a⌠ linδ time« ╔ havσ two¼ namel∙ MACRO-8░ anΣ LINK-8░ froφ Microsof⌠ ì anΣ ASMBL/┌ anΣ LINK/┌ froφ Ithacß InterSystem≤ bu⌠ ╔ havσ n∩ doub⌠ tha⌠ therσ ì arσ other≤ whicΦ wil∞ worδ jus⌠ a≤ well. Thσá essencσ oµ thσ schemσ i≤ t∩ le⌠ thσ linke≥ d∩ thσ worδ oµ puttinτ thσ re-ì locatablσ codσ iε thσ righ⌠ spo⌠ rathe≥ thaε doinτ tw∩ assemblies¼á anΣ t∩ usσ ì a program to match the two code images and append a bitmap. ┴ certaiε disciplinσ i≤ requireΣ wheε codinτ ß prograφ whicΦ wil∞ late≥ becomσ ì self-relocating«á Thi≤á disciplinσá ha≤á n∩ effec⌠ oε thσá executioεá oµá thσ ì program but provides information to the relocator module. ▒ AvoiΣ thσ usσ oµ "absoluteó prograφ segments╗ the∙ arσ no⌠ necessar∙ ì anΣá unles≤á yo⌡ arσ VER┘ careful¼á wil∞ interferσ witΦ thσá linkinτ ì order. 2 Fo≥á thσ benefi⌠ oµ thσ relocato≥ modulσ thσ firs⌠ tw∩ item≤ iεá thσ ì áááááááááárelocatable program must be: áááááááááááááááa)áááßá worΣá containinτá thσ addres≤á oµá thσá firs⌠ ì áááááááááááááááááááácharacter past the end of the program, èáááááááááááááááb)áááßá jum≡á t∩ thσ entr∙ poin⌠ oµá thσá relocatablσ ì ááááááááááááááááááááprogram segment. MACRO-80 Example: .Z80 ;I always use Zilog mnemonics cr equ 0dh lf equ 0ah ;These statements don't generate ckpt equ 144 ;any code so they can go here zap macro field,len . . . endm dseg ;Normally the first loaded $memry:: defs 2 ;Address of end of program j≡áá start ;Used and modified by relocator ;Rest of program as it would normally be written. . . . Start: . . . end start ááááááááááIteφá (a⌐ i≤ useΣ b∙ thσ relocato≥ modulσ t∩ calculatσ thσ lengtΦ oµ ì ááááááááááthσ relocatablσ prograφ segmen⌠ anΣ thencσ t∩ determinσ thσá addres≤ ì áááááááááát∩á whicΦ t∩ movσ thσ relocatablσ code«á Thσ worΣ itselµ wil∞ no⌠ bσ ì áááááááááárelocated. Iµá yo⌡ arσ usinτ thσ Microsof⌠ assemble≥ anΣ linke≥ theεá iteφá (a⌐ ì áááááááááácan be a source statement of the form: $MEMRY:: defs 2 ááááááááááa≤á iεá thσ abovσ examplσ anΣ LINK-8░ wil∞ kindl∙ fil∞ thσ worΣá in« ì ááááááááááLINK/┌á doesn'⌠ providσ thi≤ conveniencσ s∩ usσ ßá sourcσá statemen⌠ ì áááááááááálike: dw $END$ wherσá $ENDñá i≤ ß labe∞ declareΣ jus⌠ beyonΣ thσ las⌠ bytσá iεá thσ ì ááááááááááprogram«á (Makσá surσ tha⌠ i⌠ i≤ iε thσ last-loadeΣ segmen⌠ oµá thσ ì áááááááááálast-linked module!) Thσá relocato≥á prograφ extract≤ thσ addres≤ fielΣ oµ iteφ (b⌐á and¼ ì ááááááááááwheεá i⌠á ha≤ completeΣ thσ relocation¼á transfer≤ contro∞á t∩á tha⌠ ì ááááááááááaddres≤ iε thσ relocateΣ codσ segment«á Iε thσ meantime¼ thσ targe⌠ ì ááááááááááoµá thσ jum≡ instructioε i≤ modifieΣ t∩ jum≡ t∩ thσ BDO╙á whilσá thσ ì áááááááááájum≡á a⌠ addres≤ ╡ i≤ modifieΣ t∩ jum≡ t∩ thi≤ instructioε s∩ tha⌠ ß ì ááááááááááprogram loaded into low memory sees a smaller TPA. ááááááááááConfused┐á Perhap≤á anothe≥á examplσ wil∞ help«á Supposσá tha⌠á wσ ì áááááááááárelocatσá ß prograφ whicΦ i≤ 42BΦ byte≤ lonτ anΣ thσ BDO╙ start≤á a⌠ ì ááááááááááC200h« Beforσ relocation¼ thσ scenari∩ i≤ somethinτ likσ this: è 0005 JP C200 Jump into BDOS . . . 0100 Start of relocator module . . . 01FE DEFW 062B Address of first byte past program 0200 JP NTRYPT Jump to entry point of relocatable program segment . . . 02A7 NTRYPT: Program start address . . . 062A Last byte of program 062B Start of bitmap . . . C200 BDOS After relocation things will be a little different: 0005 JP BD00 Indirect jump to BDOS . . . BD00 JP C200 Actual jump into BDOS . . . BDA7 NTRYPT: Relocator exits to this address . . . C12A End of program . . . C200 BDOS Providinτá tha⌠ ß prograφ ha≤ thσ requireΣ item≤ coded¼á i⌠ caεá bσá converteΣ ì into a self-relocating program without re-assembly. The steps are: 1ááááGeneratσ ß .CO═ filσ b∙ linkinτ thσ relocato≥ modulσ anΣ relocatablσ ì áááááááááácodσá segment«á Specif∙ ß loaΣ addres≤ oµ 01F┼ fo≥ thσá relocatablσ ì áááááááááácodσ segment« 2 Generatσá anothe≥á .CO═ filσ b∙ linkinτ onl∙á thσá relocatablσá codσ ì áááááááááásegment specifying a load address of 02FE. 3 Run the RELOC program to generate the self-relocating program. Ste≡á ▒á effectivel∙á concatenate≤ thσ relocato≥ modulσá anΣá thσá relocatablσ ì prograφá segment«á Thσ linke≥ put≤ thσ pointe≥ t∩ thσ enΣ oµ thσá prograφá a⌠ ì (01FF,01FE⌐á anΣ thσ jum≡ instructioε a⌠ 0200«á Thσ relocato≥ modulσ caε theε ì finΣá thσ prograφ star⌠ addres≤ a⌠ (0202,0201)«á Notσ tha⌠ thσ end-of-prograφ ì pointer does not become part of the relocated program. Ste≡ ▓ create≤ ß seconΣ imagσ oµ thσ relocatablσ prograφ segmen⌠ sucΦ tha⌠ al∞ ì addresses differ by 100h from those in the file created in step 1. Step 3 adds a bitmap. No⌠á onl∙ arσ therσ fewe≥ step≤ thaε iε thσ GENMO─ anΣ REL.UT╠ method≤ bu⌠á n∩ ì modificatioε t∩ thσ prograφ sourcσ codσ i≤ necessar∙ anΣ thσ wholσ proces≤ caε ì be performed without operator intervention with a .SUB file like this: :Generate a self-relocating version of the $1 program è L80 reloc,/p:1fe,$1,Org200/n/e L80 /p:2fe,$1,Org300/n/e RELOC $1 ERA org?00.com where $1 will be substituted by the name of the program. Something like: SUBMIT RELOC RP doe≤ i⌠ allíá Easy«á Oncσ ╔ decideΣ ho≈ i⌠ coulΣ bσ done¼á implementatioε oµ ì thσá SRP-generatioεá schemσ tooδ ß hel∞ oµ ß lo⌠ les≤ timσ thaεá writinτá thi≤ ì documentation! And that's not all... Giveεá ßá systeφ sucΦ a≤ thσ above¼á i⌠ caε bσ madσ t∩ d∩ othe≥á things«á Fo≥ ì example¼á somσ program≤ returε contro∞ t∩ thσ CC╨ wheε the∙ finisΦ insteaΣá oµ ì exitinτá t∩ CP/═ b∙ doinτ ß "warφ boot"╗á iε relocatinτ sucΦ ß prograφ t∩ higΦ ì memory¼á i⌠á woulΣ neeΣ t∩ bσ placeΣ jus⌠ belo≈ thσ CC╨ insteaΣ oµ jus⌠á belo≈ ì thσ BDOS«á Again¼á withou⌠ to∩ mucΦ effort¼á thσ systeφ caε als∩ providσá thσ ì abilit∙á fo≥ ß use≥ t∩ explicitl∙ nominatσ wherσ thσ relocateΣ prograφ codσ i≤ ì t∩á reside«á Anothe≥ worthwhilσ facilit∙ i≤ tha⌠ oµ havinτ ß prograφá overla∙ ì par⌠ oµ CP/═ itself¼á particularl∙ thσ BIOS«á Therσ i≤ no⌠ ß lo⌠ oµ rooφ oε ß ì standarΣ singlσ densit∙ flopp∙ disδ fo≥ ß BIO╙ oµ an∙ sophisticatioε bu⌠ i⌠ i≤ ì certainl∙á possiblσ t∩ overla∙ ß minima∞ BIO╙ witΦ ß self-relocatinτ onσá froφ ì thσ disk'≤ datß track≤ whicΦ caε contaiε ß hos⌠ additiona∞ features«á Perhap≤ ì aεá eveεá morσá genera∞ applicatioε fo≥ thi≤ facilit∙ i≤ tha⌠á i⌠á offer≤á thσ ì abilt∙á t∩á tes⌠ BIO╙ modification≤ withou⌠ goinτ througΦ ß serie≤á oµá systeφ ì generations. T∩á implemen⌠á thesσ extrß capabilities¼á thσ SR╨ generato≥ ha≤á t∩á recognisσ ì command-linσá directive≤á froφá thσá use≥ anΣá pas≤á thσá informatioεá t∩á thσ ì relocato≥ modulσ whicΦ iε turε mus⌠ bσ cleve≥ enougΦ t∩ ac⌠ oε it«á Thi≤ doe≤ ì impl∙á ß degreσ oµ interdependencσ betweeε thσ SR╨ generato≥ anΣ thσ relocato≥ ì modulσá iε tha⌠ thσ SR╨ generato≥ need≤ t∩ kno≈ somethinτ abou⌠ thσá structurσ ì oµá thσ relocator¼á bu⌠ ╔ believσ tha⌠ thσ sligh⌠ los≤ oµ generalit∙á i≤á wel∞ ì compensateΣ b∙ thσ extrß versatilit∙ oµ thσ package. A≤áá supplied¼áá thσá SR╨á generato≥á recognise≤á thσá followinτá command-linσ ì directives: RELOC X á Generatσá X.CO═á whicΦá wil∞ movσ itselµ u≡á t∩á jus⌠ ì ááááááááááááááááááááááááábelo≈ thσ BDOS¼ overlayinτ somσ o≥ al∞ thσ CCP« Thi≤ ì ááááááááááááááááááááááááái≤ thσ mos⌠ commoε usagσ oµ thσ SR╨ generato≥ anΣ ha≤ ì áááááááááááááááááááááááááthσ simples⌠ commanΣ string« Prograφ ╪ i≤ assumeΣ t∩ ì áááááááááááááááááááááááááreturε contro∞ t∩ CP/═ b∙ doinτ ß "warφá boot"«á Thσ ì áááááááááááááááááááááááááBDO╙á jum≡ a⌠ memor∙ location≤ ╡ througΦ ╖ i≤ altereΣ ì ááááááááááááááááááááááááát∩ reflec⌠ ß smalle≥ TP┴ size. RELOC X - ááááááááááááA≤á fo≥ thσ previou≤ commanΣ forφ excep⌠á tha⌠á X.CO═ ì áááááááááááááááááááááááááwil∞á relocatσá itselµ t∩ jus⌠ belo≈ thσ CC╨ anΣá thσ ì áááááááááááááááááááááááááBDO╙ jum≡ a⌠ locatioε ╡ wil∞ no⌠ bσá affected«á I'l∞ ì áááááááááááááááááááááááááexplain why later. RELOC X addr "Addróá i≤á ßá hexadecima∞ numbe≥ whicΦá mus⌠á bσá aε ìèááááááááááááááááááááááááámultiplσá oµá 100h«á X.CO═ wil∞ movσ itselµ t∩á tha⌠ ì áááááááááááááááááááááááááaddress. Thσá "Xó prograφ generateΣ b∙ thσ abovσ commanΣ form≤ wil∞ bσá executeΣá afte≥ ì relocatioεá ha≤á beeεá donσ anΣ thσ codinτ rule≤ describeΣá iεá thσá precedinτ ì sectioε must be obeyed for the relocation system to work. Onl∙á thσá "normalóá relocatioε t∩ jus⌠ belo≈ thσ BDO╙ cause≤á thσá BDO╙á jum≡ ì instructioεá a⌠á memor∙á location≤á 5-╖ t∩ bσ modifieΣ t∩á reflec⌠á ßá reduceΣ ì transien⌠ prograφ area«á Thσ decisioε t∩ omi⌠ thσ modificatioε iε othe≥ case≤ ì wa≤ fairl∙ arbitrar∙ bu⌠ wa≤ takeε iε thσ interes⌠ oµ generality«á ╔ diΣá no⌠ ì wisΦá t∩ imposσ an∙ restrictioε oε thσ prograφ beinτ relocateΣ anΣá considereΣ ì thσ possibilit∙ tha⌠ thσ prograφ migh⌠ rel∙ oε thσ jum≡ instructioε beinτ lef⌠ ì unchangeΣá fo≥ an∙ oµ ß variet∙ oµ reasons«á Oµ course¼á therσ i≤ nothinτá t∩ ì sto≡ thσ relocateΣ prograφ froφ modifyinτ thσ BDO╙ jum≡ itself«á Also¼á therσ ì i≤á ßá public-domaiε utilit∙ provideΣ b∙ Johε Woolne≥ fo≥ protectinτá thσá CC╨ ì froφá beinτ overlaiΣ b∙ transien⌠ program≤ s∩ tha⌠ therσ exist≤ ßá methoΣá fo≥ ì achievinτá thσ samσ resul⌠ a≤ woulΣ bσ attaineΣ b∙ havinτ thσ relocato≥ adjus⌠ ì the jump instruction: 1. Install John Woolner's CCP protection, 2. Use the command form RELOC X.COM (i.e. no second parameter). Thσá SR╨ generato≥ als∩ recognise≤ threσ variant≤ oµ anothe≥ commanΣ forφá fo≥ ì whicΦá thσ codinτ rule≤ arσ slightl∙ different«á Thσ worΣ pointinτ t∩á "freeó ì memor∙á i≤á stil∞ requireΣ bu⌠ thσ extrß jum≡ instructioε a⌠ thσ heaΣá oµá thσ ì relocatablσ codσ neeΣ not¼á anΣ generall∙ mus⌠ not¼á bσ supplied« Thσ commanΣ ì form is RELOC X CCP or RELOC X BDOS or RELOC X.COM BIOS Thσá X.CO═ filσ generateΣ b∙ thesσ command≤ wil∞ relocatσ s∩ a≤á t∩á overwritσ ì thσá CCP¼á BDO╙á o≥á BIO╙ respectively«á Contro∞ wil∞ NO╘ bσá passeΣá t∩á thσ ì relocateΣá code«á Instead¼á thσ relocato≥ modulσ wil∞ exi⌠ t∩ thσ CC╨ withou⌠ ì doinτ ß warφ boo⌠ s∩ tha⌠ thσ relocateΣ codσ wil∞ remaiε iε memory« Notσ tha⌠ ì thσá destinatioε addres≤ fo≥ thσ relocateΣ codσ i≤ calculateΣ froφ thσá targe⌠ ì oµá thσ jum≡ instructioε a⌠ memor∙ locatioε ╡ anΣ wil∞ bσ wronτ iµá tha⌠á jum≡ ì instruction has been altered. Copyright notice Thesσ program≤ havσ beeε submitteΣ t∩ thσ publiπ domaiε viß Bil∞ Bolton'≤ RCP═ ì systeφ anΣ comprisσ ß systeφ fo≥ simpl∙ generatinτ self-relocatinτ program≤ b∙ ì ßá methoΣ whicΦ relie≤ oε ß linke≥ t∩ generatσ tw∩ objec⌠ codσ file≤ whicΦ arσ ì theεá processeΣ t∩ yielΣ aε objec⌠ prograφ consistinτ oµá ßá relocator¼á user-ì supplieΣá objec⌠á codσá anΣá ß relocatioεá bitmap«á Thesσá program≤á anΣá thσ ì accompanyinτá documentatioε ma∙ bσ freel∙ distributeΣ iε origina∞ o≥á modifieΣ ì forφ subjec⌠ t∩ thσ followinτ conditions: 1.áááAlthougΦá therσ i≤ n∩ restrictioε oε thσ salσ oµ self-relocatinτ program≤ ì ááááágenerateΣá b∙á thσ methoΣ describeΣ herein¼á thesσ program≤á o≥á variant≤ ì áááááthereoµá ma∙ no⌠ bσ solΣ a≤ par⌠ oµ an∙ prograφ packagσá withou⌠á writteε ì ááááápermissioεá froφ thσ author«á Neithe≥ ma∙ an∙ prograφ o≥ prograφ packagσ ì áááááwhicΦá i≤ dependen⌠ fo≥ it≤ operatioε oε thσ usσ oµ thi≤ methoΣá bσá solΣ ì áááááwithou⌠á sucΦ permission«á Iε othe≥ word≤ yo⌡ ma∙á sel∞á self-relocatinτ ìèáááááprograms but not the method of generating them. 2.áááThσá author'≤á namσá mus⌠á bσ retaineΣ iε al∞ sourcσá codσá (origina∞á o≥ ì ááááámodified⌐á anΣá a≤ aε acknowlegemen⌠ iε an∙ messagσá displayeΣá b∙á thesσ ì áááááprogram≤ o≥ variant(s⌐ thereof« Aε acknowledgemen⌠ givinτ credi⌠ fo≥ thσ ì ááááámethoΣá shal∞ contaiε thσ author'≤ namσ o≥ thσ word≤ "H-┬ methodó o≥á thσ ì áááááwords "Ashby method". 3.áááThi≤ copyrigh⌠ noticσ mus⌠ bσ includeΣ iε anΣ retaineΣ iε al∞ sourcσ codσ ì áááááand documentation pertaining to this system. John Hastwell-Batten 38 Silvia Street Hornsby NSW 2077 AUSTRALIA (02) 477 4225 1st November, 1982 Acknowledgement Iεá testinτ thosσ relocation≤ whicΦ overla∙ specifieΣ portion≤ oµ CP/═ ╔á havσ ì madσá usσ oµ Johε Woolner'≤ CC╨ protectioε scheme obtaineΣ vißá Bil∞á Bolton'≤ ì RCP═á system«á Withou⌠á thσ CC╨ protectioε thσ verificatioε oµ thσá relocato≥ ì modulσá woulΣ havσ beeε exceedingl∙ difficul⌠ a≤ thσ standarΣ prograφá testinτ ì tool≤á al∞á overla∙á thσ CC╨ which¼á iε thσ casσ oµá thσá CP/═á overlays¼á thσ ì relocator expects to be intact. èSYSTEM PROGRAMS AND FILES Therσá arσ ß lo⌠ oµ thing≤ calleΣ "RELOCó iε thi≤ systeφ anΣ thσ variou≤ file≤ ì arσá distinquisheΣá b∙ thσ filenamσ extension«á Thσ actua∞ SR╨á generato≥á i≤ ì writteεá iεá BDS-├á bu⌠ i⌠ coulΣ equall∙ (o≥ almos⌠á equally⌐á bσá writteεá iε ì anythinτá else«á Thσ relocato≥ modulσ i≤ writteε iε Z8░ assembl∙ languagσ anΣ ì jus⌠ abou⌠ thσ onl∙ restrictioε upoε i⌠ i≤ tha⌠ i⌠ mus⌠ bσ a⌠ mos⌠ 0FEΦá byte≤ ì long«á ╔á playeΣ arounΣ witΦ somσ funn∙ Z8░ instruction≤ whilσ ╔ wa≤á writinτ ì thσá relocato≥á anΣá neve≥á bothereΣ t∩á re-prograφá it«á (Eveεá withou⌠á thσ ì "undocumentedó Z8░ instructions¼á thσ supplieΣ codeΣ i≤ highl∙ Z8░á dependent« ì For an example of an 8080-coded relocator, see Robert van Valzah's REL.UTL) These are the files: RELOC.MAC Source of relocator module. RELOC.REL Assembled relocator module. RELOC.C BDS-C source of program generator. RELOC.COM The SRP generator. RELOC.SUB Submit file to automate the process of generating a self-relocating program. RELOC.DOC What you have been reading all this time. System also needs: M80 and L80 Microsoft's MACRO-80 assembler and LINK-80 link/loader or ASMBL/Z Ithaca InterSystems' version of the same thing and LINK/Z or any other assembler-linker combination which allows load addresses to be specified at link time. Thσá submi⌠ filσ RELOC.SU┬ i≤ se⌠ u≡ t∩ proces≤ ß prograφ comprisinτ ßá singlσ ì module. For multi-module programs just expand the linker command lines. RELOC.SU┬ wil∞ accep⌠ onσ o≥ tw∩ arguments«á Iµ supplied¼ thσ seconΣ argumen⌠ ì i≤á passeΣá t∩á thσá SR╨ generato≥ prograφ alonτá witΦá thσá (required⌐á firs⌠ ì argument. Iµá thσá SR╨ generato≥ i≤ invokeΣ witΦ n∩ argument≤ i⌠ display≤ ßá summar∙á oµ ì acceptable command forms. Thσá name≤á oµá thσ tw∩ intermediatσ .CO═ file≤ generateΣ b∙á thσá linke≥á arσ ì ORG200.CO═ anΣ ORG300.COM« Thesσ name≤ arσ hard-codeΣ int∩ thσ SR╨ generator. John Hastwell-Batten Original version and documentation: 13th October 1982 Relocation options added: 30th & 31st October 1982 Documentation updated: 1st November 1982