Re-engineering C++ Component Models Via Automatic Program Transformation

Transcription

1 Re-egieerig C++ Cmpet Mdels Via Autmatic Prgram Trasfrmati Rbert L. Akers, Ph.D. Ira D. Baxter, Ph.D. Sematic Desigs Ic. Bria J. Ellis Ke R. Luecke The Beig Cmpay Michael Mehlich, Ph.D. Abstract Autmated prgram trasfrmati hlds prmise fr a variety f sftware life cycle edeavrs, particularly where the size f legacy systems makes cde aalysis, re-egieerig, ad evluti difficult ad expesive. But cstructig highly scalable trasfrmati tls supprtig mder laguages i full geerality is itself a paistakig ad expesive prcess. This cst ca be maaged by develpig a cmm trasfrmati system ifrastructure reuseable by derived tls that each address specific tasks, thus leveragig the ifrastructure csts. This paper describes the Desig Maiteace System (DMS 1 ), a practical, cmmercial prgram aalysis ad trasfrmati system, ad discusses hw it was emplyed t cstruct a custm mderizati tl beig applied t a large C++ idustrial aviics system. The tl trasfrms cmpets develped i a 1990 s-era cmpet style t a mre mder CORBA-like cmpet framewrk, preservig fuctiality. Keywrds: sftware trasfrmati, sftware aalysis, C++, migrati, cmpet architectures, legacy systems, cmpilers, re-egieerig, abstract sytax trees, patters, rewrite rules. 1. Itrducti DMS is a mature ifrastructure fr dig aalysis ad trasfrmati f sftware based deep sematic uderstadig f prgrams. It supprts virtually all cvetial sftware laguages ad ca be applied t systems built frm multiple cdig ad desig laguages. The Beig Migrati Tl (BMT), built usig the DMS ifrastructure, autmatically trasfrms the cmpet framewrk f a large C++ aviics system frm a 1990 s era mdel t e based 1 DMS is a registered trademark f Sematic Desigs Ic. a prprietary variat f the Cmm Object Resurce Brker Architecture (CORBA), preservig fuctiality but itrducig regular iterfaces fr iter-cmpet cmmuicati. We describe the DMS ifrastructure ad the BMT applicati itself t prvide isight it hw trasfrmati techlgy ca address sftware aalysis ad evluti prblems where scale, cmplexity, ad custm eeds are barriers. We illustrate sme f the kids f sytheses ad trasfrmatis required ad sme f the issues ivlved with trasfrmig idustrial C++ cde. We als discuss the develpmet experiece, icludig the strategies fr apprachig the scale f the migrati, the style f iteracti that evlved betwee the tlbuildig cmpay ad its idustrial custmer, ad hw the prject adapted t chagig requiremets. We preset Beig s assessmet f the prject, assess the retur ivestmet f the autmated migrati strategy, ad preset sme reflectis the experiece t guide thers csiderig large scale cde re-egieerig prjects. 2. The DMS Sftware Reegieerig Tlkit DMS prvides a ifrastructure fr sftware trasfrmati based deep sematic uderstadig f prgrams. Prgrams are iteralized via DMSgeerated parsers that exist fr virtually all cvetial laguages. Aalyses ad maipulatis are perfrmed abstract sytax tree (AST) represetatis f the prgrams, ad trasfrmed prgrams are prited with prettypriters fr the apprpriate laguages. The Tlkit ca accept ad simultaeusly utilize defiitis f multiple, arbitrary specificati ad implemetati laguages (dmais) ad ca apply aalyses ad trasfrmatis t surce cde writte i ay cmbiati f defied dmais. Trasfrmatis may be either writte as prcedural cde r expressed as surce-t-surce rewrite rules i a eriched sytax

2 fr the defied dmais. Rewrite rules may be ptially qualified by arbitrary sematic cditis. The DMS Tlkit ca be csidered as extremely geeralized cmpiler techlgy. It presetly icludes the fllwig tightly itegrated facilities: A hypergraph fudati fr capturig prgram represetatis (e.g., ASTs, flw graphs, etc.) i a frm cveiet fr prcessig. Cmplete iterfaces fr prcedurally maipulatig geeral hypergraphs ad ASTs. A meas fr defiig laguage sytax ad derivig parsers ad prettypriters fr arbitrary ctext Surce Files (Dmai Ntati) Parser Defiiti Dmai Defiiti Reader Laguage Descriptis Aalysis + Trasfrm Descriptis = Tl Defiiti free laguages t cvert dmai istaces (e.g. surce cde) t ad frm iteral frms. Supprt fr ame ad type aalysis ad defiig ad updatig arbitrary amespaces ctaiig ame, type, ad lcati ifrmati with arbitrary scpig rules. Attribute evaluati fr ecdig arbitrary aalyses ver ASTs with rules tied t grammar elemets. A AST-t-AST rewritig egie that uderstads algebraic prperties (e.g., assciativity, cmmutativity). The ability t specify ad apply surce-t-surce prgram trasfrmatis based laguage sytax. Such trasfrms ca perate withi a laguage r acrss laguage budaries. A prcedural framewrk fr cectig these pieces ad addig arbitrary cde. The DMS architecture is illustrated i Figure 1. Ntice that the ifrastructure supprts multiple dmai tatis (surce cde laguages), s that multiple laguages ca be hadled r geerated by a give tl. We are presetly implemetig a geeral scheme fr capturig arbitrary ctrl flw graphs (icludig exceptis, ctiuatis, parallelism ad asychry) ad carryig ut data flw aalyses acrss such graphs. Our gal is t build scalable ifrastructure, e aspect f which is supprt fr cmputatial scale. DMS is implemeted i a parallel prgrammig laguage, PARLANSE [13], which eables DMS t ru cmmdity x86 symmetric-multiprcessig wrkstatis. C++ is amg the may dmais implemeted withi DMS, ad the system ctais cmplete preprcessrs, parsers, ame ad type reslvers, ad prettypriters fr bth the ANSI ad Visual C dialects. Ulike a cmpiler preprcessr, the DMS C++ preprcessr preserves bth the rigial frm ad expaded maifestati f the directives withi the AST s that prgrams ca be maipulated, Lexers/ Parsers Aalyzers Trasfrms Prcedures Cmpiler Data Structures Sequecig; Trasfrms Symbl Table Declaratis Attribute Evaluatrs Trasfrmati Egie Prettypriter Defiitis Figure 1 The DMS architecture Cmpiler Structures Prettypriters Viewer Revised Surce Files Debug Text trasfrmed, ad prited with preprcessr directives preserved, eve ctaiig preprcessr cditials. The C++ ame ad type reslver has bee exteded t fully supprt preprcessr cditials, creatig a symbl table with cditial etries fr symbls ad cditial relatiships betwee lexical scpes ctaiig such symbls. DMS has bee uder develpmet fr ie years. As presetly cstituted, it has bee used fr a variety f large scale cmmercial activities, icludig crssplatfrm migratis, dmai-specific cde geerati, ad cstructi f a variety f cvetial sftware egieerig tls implemetig tasks such as dead/cle cde elimiati, test cde cverage, executi prfilig, surce cde brwsig, ad static metrics aalysis. A mre cmplete verview f DMS is preseted i [5], icludig discussi f hw DMS was extesively used t create itself. Fr example, the DMS lexer geeratr, prettypriter geeratr, ad its ame ad type resluti aalyzers fr varius laguages are all tls created with DMS. Varius ther DMS-based tls are described the Sematic Desigs Ic. (SD) web site [16]. 3. The Beig Migrati Tl Beig's Bld Strke aviics cmpet sftware architecture is based the best practices f the mid- 1990's [17]. Cmpet techlgy has sice matured, ad the Cmm Object Resurce Brker Architecture (CORBA) cmpet mdel has emerged as a stadard. The U.S. Gvermet's Defese Advaced Research Prjects Agecy's Prgram Cmpsiti fr Embedded Systems (DARPA-PCES) prgram ad the Object Maagemet Grup (OMG) are spsrig develpmet f a CORBA-ispired stadard real time embedded system cmpet mdel (CCMRT) [8], which ffers

3 stadardizati, imprved iterperability, superir ecapsulati, ad iterfaces fr gig develpmet f distributed, real time, embedded systems like Bld Strke. Stadardizati als prvides a base fr tls fr desig ad aalysis f such systems, ad fr easier itegrati f ewly develped techlgies such as advaced schedulers ad telecmmuicati badwidth maagers. Beig wishes t upgrade its airframe sftware t a mre mder architecture, a prprietary CCMRT variat kw as PRiSm (Prduct lie Real Time embedded System). This will allw mre regular iterperability, stadardizati acrss flight platfrms, ad pprtuities fr itegratig emergig techlgies that require CORBA-like iterfaces. Yet sice the legacy sftware is peratig i mature flight evirmets, maitaiig fuctiality is critical. The mderizati effrt, the, must t alter fuctiality as it melds legacy cmpets it the mder cmpet framewrk. The task f cvertig cmpets is straightfrward ad well uderstd, but a great deal f detail must be maaged with rigrus regularity ad cmpleteess. Sice Bld Strke is implemeted i C++, the cmplexity f the laguage ad its Facet : Offered service Receptacle : Outbud iterface Evet Sik : Trigger Evet Surce : Sigal Rutime Wirig preprcessr requires careful atteti t sematic detail. With thusads f legacy cmpets w fielded, the sheer size f the migrati task is a extrardiary barrier t success. With the use f C++ libraries, apprximately 250,000 lies f C++ surce ctributes t a typical cmpet, ad a sud uderstadig f a cmpet's ame space requires cmprehesi f all this cde. T deal with the scale, sematic sesitivity, ad regularity issues, DARPA, Beig, ad SD decided t autmate the cmpet migrati usig a custm DMS-based tl. DMS, with its C++ frt ed cmplete with ame ad type resluti, its uique C++ preprcessr, its trasfrmati capability, ad its scalability, was a uiquely qualified substrate fr cstructig a migrati tl that bleded cde sythesis with cde rergaizati. Autmatig the migrati prcess assures regularity f the trasfrmati acrss all cmpets ad allws the examiati f trasfrmati crrectess t fcus primarily the geeral trasfrms rather tha C m p e t A particular, ptetially idisycratic examples. It als esures a uifrm treatmet i a variety f ways icludig ame cvetis fr ew etities, cmmetig cvetis, cde layut, ad file rgaizati. Figure 2 diagrams the relatiship f cmmuicatig CORBA cmpets. Facets are classes that prvide related methds implemetig a service, i.e., a area f fuctial ccer. Evet siks prvide etry pits fr sigalig chages f state upstream, t which the cmpet may wish t react. A similar iterface exists fr utgig calls, with evet surces beig a stadard rute thrugh which the demad fr service is sigaled t ther cmpets, ad receptacles prvidig cectis t the istaces f facets fr ther cmpets. Cmpets are wired tgether at cfigurati time, prir t system executi. receptacle C m p e t B Methd calls evet surce Evets facet evet sik C m p e t Figure 2- CORBA cmpet relatiships While evet siks ad facets are very similar ideas with respect t data flw, they are distict i the CORBA mdel fr several reass. The fuctiality f a facet is specific t each facet ad cmpet ad t the services it ffers, ad facets share little cmmality i frm r fucti with each ther r with facets f ther cmpets. Evet siks, the ther had, implemet a stadard prtcl fr itercmpet evet sigalig. Thugh the cde specifics vary with the cmpets fuctial iterfaces, the fucti, style, ad structure f evet siks are csistet acrss all cmpets, ad hece they are give distict, stylized idetity ad treatmet, likewise fr evet surces ad receptacles. The legacy cmpet structure is essetially flat, with all a cmpet s methds typically cllected i a very few classes (fte just e), each defied with.h ad.cpp files. Oe pricipal piece f the migrati ivlves factrig a cmpet it facets, each frmig a distict class ppulated with methds

4 reflectig a particular area f ccer. Other classes, like the evet siks ad receptacles, must be sythesized at a mre fie-graied level, extractig cde fragmets r cecti ifrmati frm the legacy system. Factrig a cmpet it fuctial facets requires huma uderstadig. Essetially, the legacy iterface methds must be srted it bis crrespdig t the facets, ad idicative ames give t the ew facet classes. T prvide a clea specificati facility fr the Beig egieers usig the BMT, SD develped a simple facet specificati laguage. Fr each cmpet, a egieer ames the facets ad uiquely idetifies which methds (via simple ame, qualified ame, r sigature if ecessary) cmprise its iterface. The bulk f the migrati egieer's cdig task is frmulatig facet specificatis fr all the cmpets t be migrated, a very easy task fr a kwledgeable egieer. The facet laguage itself is defied as a DMS dmai, allwig DMS t autmatically geerate a parser frm its grammar ad t defie specificati prcessig tls as attribute evaluatrs ver the facet grammar. Figure 3 shws a facet specificati fr a simple, twfacet cmpet. The list f legacy classes prescribe which classes are t be trasfrmed as part f the cmpet. Façade declaratis specify the legacy classes i which the facet iterface methds appear. Facet methd parameters eed be supplied ly t select frm verladed methds. Figure 4 illustrates the essetial factrig f the mlithic legacy class it CORBA/PRiSm facets (but des t reflect the activity related t evet siks, receptacles, r ther ew PRiSm classes.) The methds idetified i the egieer s facet specificati are relcated it ew facet classes. Refereces frm withi thse methds t utside etities are mdified with additial piters t reslve t the rigially iteded etities. Furthermre, refereces i the rest f the system t the relcated methds are als adjusted via a idirecti t pit it the ew facet classes. Declaratis f all these ew piters must appear i the apprpriate ctexts, alg with #iclude directives t prvide the ecessary amespace elemets. The BMT traslates cmpets e at a time. Iput csists f the surce cde, the facet specificati fr the cmpet beig traslated, ad facet specificatis fr all cmpets with which it cmmuicates, plus a few bkkeepig directives. Cversi iput is succict. The BMT s migrati prcess begis with the parsig f all the facet specificatis relatig t the cmpet. A DMS-based attribute evaluatr ver the facet dmai traverses the facet specificatis' abstract COMPONENT AV_LgicalPsiti_StateDevice FACET AV_LgicalPsiti_IteralStatus FACET AV_LgicalPsiti_StateMde LEGACYCLASSES AV_LgicalPsiti_StateDevice END COMPONENT FACET AV_LgicalPsiti_IteralStatus FACADE AV_LgicalPsiti_StateDevice "IsIitDataRequested" "IsAlmaacRequested" "IsDailyKeyIUseVerified" "IsDailyKeyIUseIcrrect" "IsGUV_User" "IsReceiverCtaiKeys" "GetMissiDurati" "IsRPU_Failed" "GetMemryBatteryLw" "GetReceiverLRU_Fail" END FACET FACET AV_LgicalPsiti_StateMde FACADE AV_LgicalPsiti_StateDevice "bl GetBIT_Status ()" "GetPsiti_StateRequested" "GetPsiti_StateAchieved" "GetEvetSupplierReferece" END FACET Figure 3 - Facet specificati example sytax trees ad cllates it it a database f facts fr use durig cmpet trasfrmati. After prcessig the facet specificatis, the BMT parses ad des full ame ad type resluti the C++ surce cde base, icludig files refereced via #iclude. These wuld aturally iclude the files fr the façade classes f the eighbrig cmpets. The DMS C++ ame ad type reslver cstructs a symbl table fr the etire surce base, allwig lkup f idetifiers ad methds with respect t ay lexical scpe. Oly by iteralizig the etire cde base i this maer ca symbl lkups ad the trasfrmatis depedig them be guarateed sud. This is e key pit that defeats scriptig laguages fr writig C++ trasfrmers. Fur particular kids f trasfrmatis typify what the BMT des t perfrm the cmpet migrati: New classes fr facets ad their iterfaces are geerated based the facet specificatis. The BMT geerates a base class fr each facet, essetially a stadard frm ad a "wrapper" class iheritig frm the facet ad ctaiig e methd fr each methd i the fuctial facet's iterface (i.e., fr each methd listed i the facet specificati). These wrapper methds simply relay calls t the crrespdig methd i the cmpet's legacy classes. Cstructig the

5 class h1 { h1r h1f( ) { class h2 { h1r h2f( ) { class Radar { h1 x; h2 y; r1 m1( ) { h1f(x) h2f(y) vid m2( ) { m 3(y) h1f(x) r3 m3( ) { m 1(y) vid tify() { m2(x,y) Legacy cmpet with mlithic API BMT cm pet Radar: facet APIe { x; m1; facet APItw { m2; m3; Cmpet mderizati specificati class API1facet { h1 x; Radar* cmpet; API1facet(Radar *radar){ cmpet=radar; r1 m1( ) { h1f(x) h2f(cmpet->y) class API2facet { Radar* cmpet; API2facet(Radar *radar){ cmpet=radar; vid m2( ) { m3(cm pet->y) h1f(cmpet-> APIe->x) r3 m3( ) { cmpet-> APIe->m 1( cmpet->y) class Radar { h2 y; API1facet* APIe; API2facet* APItw; Radar(){ APIe=ew API1facet(this); APItw=ew API2facet(this); vid tify() { APItw-> m2(apie->x,y) Figure 4 Factrig legacy classes it CORBA/PriSm facets wrapper methds ivlves replicatig each methd's header ad utilizig its argumets i the relayed call. Apprpriate #iclude directives must be geerated fr access t etities icrprated fr these purpses, as well as t access stadard cmpet ifrastructure. A est f cstructr patters expressed i the DMS patter laguage pull the pieces tgether it a class defiiti, thus sythesizig the cde frm patters. The chage frm a pure CORBA scheme like that illustrated i Figure 4 t a wrapper scheme was a majr midprject desig chage that allwed mderized cmpets t iterperate with utraslated legacy cmpets durig the lg-term mderizati trasiti. After cstructig the facets ad wrappers, the BMT trasfrms all the legacy cde calls t ay f the facets' methds, redirectig rigial methd calls the legacy class t istead call the apprpriate wrapper methd via ewly declared piters. The piter declaratis, their iitializatis, ad their emplymet i access paths are all iserted usig surce-t-surce trasfrms, the latter with cditials t fcus their applicability. A example f e such trasfrm appears i Figure 5. The varius argumets are typed by their crrespdig C++ grammar termial ames, ad the rule trasfrms e pstfix_expressi t ather. Withi the bdy f the rule, argumet ames are preceded by "\". The rule uses ccateati t cstruct the symbl fr CORBA-style cmpet with faceted subapis the ew piter ad adds the idirecti. It will be applied ly whe the "piter_refers" predicate establishes that the class_piter ad methd ame crrespd t a specified facet methd. If the rule des fire, it will als trigger sme tl-iteral bkkeepig as a side effect. -+ Rewrites legacy crss-cmpet methd refereces, -+ e.g., Cmp1->methame(arg1, arg2) rewrites t -+ Cmp1BarFacetPtr_->methame(arg1,arg2) private rule adjust_cmpet_access( class_ptr: idetifier, methd:idetifier, argumets:expressi_list): pstfix_expressi->pstfix_expressi = "\class_piter->\methd(\argumets)" -> "\ccat\(\ccat\( \get_facet_ame\(\class_piter\,\methd\)\, Facet_\)\, \class_ptr\) ->\methd(\argumets)" with side-effect remve_idetifier_table_etries (class_piter, methd) if piter_t_freig_cmpet(class_ptr). Figure 5 - DMS access path rewrite rule DMS patters ad rewrite rules are parameterized by typed AST s frm the dmai (C++). Quted frms withi the defiitis are i the dmai sytax, but withi qutes, backslashes ca precede -dmai lexemes. Fr example the refereces t the class_piter, methd, ad argumets parameters are preceded with slashes, as are refereces t the ames f ther patters (ccat ad get_facet_ame), ad sytactic artifacts f ther patter parameter lists (paretheses ad cmmas).

6 The applicati f the rewrite rule ca be made subject t a Blea cditi, as it is here by the exteral fucti piter_refers_class_f_freig_cmpet, ad may als, up applicati, trigger a side effect like exteral prcedure remve_idetifier_table_etries. Receptacle classes prvide a image f the utgig iterface f a cmpet t the ther cmpets whse methds it calls. Sice a particular cmpet's cectivity t ther cmpets is t kw at cmpile time, the receptacles prvide a wirig haress thrugh which dyamic cfigurati cde ca cect istaces it a flight cfigurati. Cstructig the receptacles ivlves searchig all f a cmpet's classes fr utgig methd calls, idetifyig which facet the called methd belgs t, ad geeratig cde t serve each cecti accrdigly. Figure 6 illustrates a prti f a receptacle.cpp file. The figure illustrates e f the Cect methds, which are always f the same frm, but which draw specifics frm the callig evirmet ad the specifics f the legacy methd. The BMT creates iclude directives apprpriate t the callig ad called cmpets ad as required by ther symbls appearig i the methd headers. Stadard receptacle cmmets are iserted. Evet siks are classes that are amg the cmmuicati aspects f a cmpet, represetig a etry pit thrugh which a evet service ca deliver its prduct. They are uifrm i style ad structure fr all cmpets i a way that is mre r less idepedet f the cmpets fuctiality, but their ctet is evertheless drive by the legacy cde s particular itercectivity behavir. Sice the essetial cde fragmets fr evet prcessig already exist i the legacy classes (thugh their lcatis are t specified t the BMT ad cat geerally be characterized), sythesizig evet siks ivlves havig the BMT idetify idimatic legacy evet-hadlig cde thrughut the legacy cmpet by matchig agaist DMS patters fr thse idims. Cde thus idetified is mved it the ew evet sik class, which is sythesized with a stadard framewrk f cstructive patters. Ctrl structures are the merged t cslidate the hadlig f each specific kid f evet. Oe ecessary cmplicati f this extesive mvemet f cde frm e lexical evirmet t ather is that all relevat ame space declaratis must be cstructed i the ew evet sik. Defiitis, declaratis, ad #iclude directives supprtig the mved cde must be cstructed i the evet sik class, ad ewly irrelevat declaratis must be remved frm the rigial evirmet. Dig all this requires extesive use f the DMS symbl table fr the applicati, which amg ther thigs retais kwledge f the lcatis withi files f the declaratis ad defiitis f all symbls. Evet sik cde extracti ad sythesis cmbies patter-based recgiti f idimatic frms with amespace ad cde rergaizati ad simplificati via sematically ifrmed trasfrmati. The BMT, the, sigificatly mdifies the legacy classes fr the cmpet by extractig cde segmets, by mdifyig access paths, by remvig cmpet piter declaratis ad iitializatis, by addig facet piter declaratis ad iitializatis, by recfigurig the amespace as ecessary, ad by dig ther miscellaeus mdificatis. It als itrduces ew classes fr the cmpet s facets, facet wrappers, receptacles, evet siks, ad a // File icrprates PRiSm Cmpet Mdel (Wrapper versi) // file geerated by the BMT tl fr the PCES II Prgram #iclude "AMV LgicalPsiti_StateDevice/AMV LgicalPsiti_StateDevice.h" #iclude "AMV LgicalPsiti_StateDevice/AMC Psiti1Receptacle.h" #iclude "AMV LgicalPsiti_StateDevice/AMC Psiti1Wrapper.h" AMC Psiti1Receptacle::AMC Psiti1Receptacle( AMV LgicalPsiti_StateDevice * theamv LgicalPsiti_StateDevicePtr) : theamv LgicalPsiti_StateDevicePtr_(theAMV LgicalPsiti_StateDevicePtr) { //There is thig t istatiate. AMC Psiti1Receptacle::~AMC Psiti1Receptacle() { //Nthig eeds t be destructed. bl AMC Psiti1Receptacle::CectAMV LgicalPsiti_StateDevice ( BM Facet *item) { // Cast the parameter frm a BM Facet piter t a wrapper piter if (AMC Psiti1Wrapper *tempcmpptr = platfrm_depedet_d_dyamic_cast<amc Psiti1Wrapper *>(item)) { theamv LgicalPsiti_StateDevicePtr_ -> AddAMC Psiti1Cecti(tempCmpPtr); retur true;... Figure 6 - A prti f a geerated receptacle.cpp file

7 equivalet iterface class desired by Beig cmpet desigers. Each kid f ew class has a regular structure, but the details vary widely, based the characteristics f the cmpet beig traslated. Sme classes, like the evet siks, are ppulated with cde fragmets extracted frm the legacy class ad assembled it ew methds uder sme cllati heuristics. I ur experiece, the amut f ew r mdified cde the BMT prduces i a cverted cmpet amuts t ver half the amut f cde i the legacy cmpet. Sice a typical cmpetbased system ivlves a large umber f cmpets, this makes a clear ecmy-f-scale argumet fr usig autmatic trasfrmati i cmpet reegieerig. 4. Experiece Beig has extesive expertise i aviics ad cmpet egieerig, but ly a ascet appreciati f trasfrmati techlgy. The tl builder, Sematic Desigs, uderstads trasfrmati ad the mechaized sematics f C++, but had ly cursry prir uderstadig f CORBA cmpet techlgy ad aviics. Other peratial issues i the cversi were the strict prprietary ature f mst f the surce cde, ucertaity abut what extic C++ features might tur up i the large surce cde base, Beig s evlvig uderstadig f the details f the target cfigurati, ad the gegraphical separati betwee Beig ad SD. T deal with mst f these issues, Beig chse a particular -prprietary cmpet ad perfrmed a had cversi, thus prvidig SD with a ccrete image f surce ad target ad a bechmark fr prgress. The had cversi frced details it Beig's csiderati. New requiremets develped i mid-prject, mdifyig the target ( e ccasi very sigificatly). The flexible DMS apprach allwed SD t adjust the tl accrdigly ad with maageable rewrkig. Had a maual cversi altered its curse at the same pit, the cst fr recdig cde that had already bee prted wuld have bee very high. Beig uburdeed by applicati kwledge, SD was able t fcus purely traslati issues, remvig frm the cversi edeavr the temptati t make applicati-related adjustmets that culd add istability. Electric cmmuicati f bechmark results prvided a basis fr gig evaluati, ad phe cfereces supprted develpmet f sufficiet bilateral uderstadig f tl ad cmpet techlgies, miimizig the eed fr travel. SD's lack f access t the full surce cde base required the tl builders t prepare fr wrst case scearis f what C++ features wuld be ecutered by the BMT i the larger surce base. This frced develpmet f SD's C++ preprcessig ad ame resluti ifrastructure t hadle the crss prduct f preprcessig cditials, templates, ad macrs. These imprvemets bth hardeed the tl agaist uaticipated stress ad stregtheed the DMS ifrastructure fr future prjects. 5. Evaluati Beig used the BMT t cvert tw large cmpets hadlig avigati ad lauch area regi cmputatis t the PRiSm Cmpet Mdel fr use i the successful DARPA PCES Flight Demstrati i April, Tl iput was extremely easy t frmulate. Oe script, which culd be shared amg all cmpets, set evirmet variables guidig the tl it the surce cde base ad the ivked the tl. Frmulatig cmpet-specific iput tk geerally arud 20 miutes per cmpet. This time cmmitmet culd be less fr smaller cmpets ad fr egieers mre experieced usig BMT. The BMT cverts e cmpet at a time. (A batch file culd very easily be writte t cvert multiple cmpets at ce). Usually the tl wuld execute fr apprximately te miutes a Dell 610 Precisi Desktp with dual prcessr, prducig a reegieered cmpet ready fr pst-prcessig by the huma egieer. The geerated ad mdified cde cfrmed t Beig's style stadards ad was free f irregularities ad errrs. Huma egieers did a mdest amut f hadfiishig, mstly i situatis uderstd i advace t require huma discreti. I these cases, the tl highlighted the geerated cde with cmmets recmmedig sme particular acti ad smetimes geerated cadidate cde. Rughly half the time, this cadidate cde was sufficiet; ther cases required had mdificati. The mst difficult part f the cversi was the evet sik mechaizati. Fr iput cmpets that had their evet mechaizati spread acrss several classes, the BMT crrectly mved the cde fragmets it the evet siks, but the huma egieer was required t update sme cde iside the trasitied cde fragmets, makig judgemets, fr istace, abut whether sme aggregatis f cde shuld be ecapsulated i ew fuctis. These judgemet-based decisis wuld have bee ecessary with a had cversi as well. Mre extesive egieerig f the BMT might have elimiated this maual requiremet by applyig heuristics. Testig csisted f very clse cde review ad testig f the bechmark cmpet, plus visual ispecti ad cvetial testig f ther cmpets.

8 Amg the advatages f usig the BMT were: All cde was geerated the basis f a simple facet specificati. The facet specificatis were extremely easy ad quick t write. The geerated cde was always cmplete with respect t the specificatis. N egative side effects were geerated by the tl. This meas the tl did t geerate cde i places that it was t desired, r did the tl mve ay cde fragmets t places that were t desired, mistakes that scriptig appraches are mre pre t makig. The tl s ame resluti capability prved t be a majr advatage ver the scriptig appraches usually used, which fte create upredictable side effects that BMT is capable f avidig. By usig the BMT, we reduced the time ecessary t cvert the tw cmpets used fr the DARPA PCES Demstrati by apprximately half, cmpared t the time required t cvert the cmpets by had. This time cmmitmet is based the etire cversi prcess, which csists f cvertig the cmpet, pst prcessig the cmpet based the BMT-geerated cmmets, writig the cmpet s dyamic cfigurati maager by had, ad testig ad itegratig the cverted cmpet i the resultat sftware prduct. Fr a large prject with hudreds r eve thusads f cmpets a 50% reducti i ttal cversi time eables a tremedus cst ad time reducti. The tl-based apprach wuld represet the differece betwee machie-hurs ad maceturies f cde develpmet labr, betwee feasibility ad ifeasibility f mass cversi. 6. Retur Ivestmet Develpig a custm migrati tl takes a sigificat effrt. Nt icludig the DMS evirmet ctributi, the BMT required 13,000 lies f ew tl cde. This develpmet cst must be balaced agaist the alterative cst f dig the tl's wrk by had, s the tradeff fr mechaized migrati depeds predmiately the amut f cde beig prted. Fr small applicatis, the effrt is t wrthwhile, but with eve a mdest sized legacy system, the ecmics quickly tur psitive. Oe bechmark legacy cmpet cversi gives a idea f the scale f this cversi. The legacy cmpet, typical i size ad cmplexity, ctaied 9,931 lies f surce cde. The BMTcverted cmpet ctaied 9,456 lies, icludig 2,109 lies f cde i ewly geerated classes ad 2,222 mdified lies i the residual legacy classes. Scalig these umbers, t cvert a mere 60 cmpets wuld require revisi r creati f ver 250,000 lies f cde. Prtig fur such cmpets wuld cause mre ew cde t be writte tha wet it the BMT itself. With airframes typically ctaiig thusads f cmpets, the ecmic advatage f mechaized migrati is cmpellig. The BMT autmates ly the cdig part f the migrati. Testig ad itegrati are als sigificat factrs, ad sme had plishig f the BMT utput was required. Cdig time was reduced t ear zer, ad the savigs i cdig time ale allwed a reducti f apprximately half the ttal time required t migrate the cmpets used fr the DARPA PCES demstrati. The regularity f style i autmatically migrated cde prvides a less quatifiable but wrthwhile extra value. The measure f ecmic success is t whether a migrati tl achieves 100 percet autmati, but whether it saves time ad mey verall. Beig felt that cvertig 75 percet f the cde autmatically wuld prduce sigificat cst savigs, a gd rule f thumb fr mdest-sized prjects. Aythig less puts the beefit i a gray area. The cde prduced by the BMT was 95 percet t 98 percet fiished. This umber culd have bee drive higher, but the additial tl develpmet cst did t justify the dwidlig payff i this pilt prject. Cst-beefit tradeffs shuld be csidered whe scpig the task f a migrati tl, eve while the prject is i prgress. I this prject, fr example, we culd have develped elabrate heuristics fr cslidatig evet sik cde, but we judged the expese t t be wrthwhile fr the pilt prject. Ay prject f this kid wuld face similar issues. Huge prjects wuld easily justify greater refiemet f a migrati tl, resultig i less eed fr had plishig the results, ad thus drivig cdig csts ever lwer. Mechaizati ca mea the differece betwee feasibility ad ifeasibility f eve a medium size prject. 7. Techlgical Barriers Oe iheret techical difficulty is the autmatic cversi f sematically ifrmal cde cmmets. Thugh cmmets are preserved thrugh the BMT migrati, what they say may t be whlly apprpriate fr the ewly mdified cde. Develpig accurate iterpretatis f free text discussig legacy cde ad mdifyig legacy cmmets t reflect cde mdificatis wuld challege the state f the art i bth atural laguage ad cde uderstadig. S while ew dcumetati ca be geerated t accurately reflect the sematics f ew cde, legacy dcumetati must be viewed as subject t huma revisi. Thugh the DMS C++ preprcessr capability, with its special treatmet f cditials, was up t the task fr this migrati, extremely extesive use f

9 C/C++ preprcessrs explitig dialect differeces, cditials, templates, ad macrs ca lead t a explsi f pssible sematic iterpretatis f system cde ad a resurce prblem fr a migrati tl. Preservig all these iterpretatis, hwever, is ecessary fr sudess. Furthermre, sice macr defiitis ad ivcatis must be preserved as ASTs thrugh migrati, macrs that d t map clealy t ative laguage cstructs (e.g., prducig ly fragmets f a sytactic cstruct r fragmets that partially verlap multiple cstructs) are very difficult t maitai. Thugh these ustructured macr defiitis cause prblem fr cmpilers, sice they are relieved prir t sematic aalysis with respect t ay sigle cmpilati, t preserve them i the abstract represetati f a prgram fr all cases is quite difficult. All these factrs suggest that fr sme prjects usig laguages ivlvig preprcessrs, a cleaup f preprcessr cde prir t system migrati is i rder. Fr reass f scale ad cmplexity, this is a separate prblem that culd be tackled with ather autmated, custmized tl. 8. Observatis A few ver-archig bservatis apply t this ad ther mass trasfrmati prjects: Mass migratis are best t migled with chages i busiess lgic, ptimizati, r ther sftware ehacemets. Etaglig tasks muddies requiremets, iduces extra iteracti betwee tl builders ad applicati specialists, ad makes evaluati difficult, at the expese f sudess, time, ad mey. Related tasks may be csidered idepedetly, applyig ew trasfrmati tls if apprpriate. Autmatig a trasfrmati task helps deal with chagig requiremets. Mdifyig a few rewrite rules, cstructive patters, ad rgaizatial cde is far easier ad results i a mre csistet prduct tha revisig a mass f had-traslated cde. Chages implemeted i the tl may maifest i all previusly migrated cde by simply re-ruig the mdified tl the rigial surces. This allws bledig the requiremets defiiti timeframe it the implemetati timeframe, which ca sigificatly shrte the whle prject. Clealy factrig a migrati task betwee tl builders ad applicati specialists allws prprietary ifrmati t remai withi the applicati wer s rgaizati while frcig tl builders tward ptimal geerality. Lack f access t prprietary surces, r i geeral lack f full visibility it a custmer s prject iduces trasfrmati egieers t aticipate prblems ad cfrt them i advace by buildig rbust tls. Surprises therefre ted t be less verwhelmig. Autmated trasfrmati allws the cde base t evlve idepedetly durig the migrati tl develpmet effrt. T get a fial prduct, the tl may be re-ru the mst recet surce cde base at the ed f tl develpmet. There is eed fr parallel maiteace f bth the fielded system ad the system beig migrated. Usig a mature ifrastructure makes the cstructi f trasfrmati-based tls t just ecmically viable, but advatageus. Nt dig this is ifeasible. Laguage frt eds ad aalyzers, trasfrmati egies, ad ther cmpets are all very sigificat pieces f sftware. The BMT ctais apprximately 1.5 milli lies f surce cde, but mst is DMS ifrastructure. Oly 13,000 lies f cde are BMTspecific. Furthermre, ff-the-shelf cmpets are iadequate t the task. Fr example, lex ad yacc d t prduce ASTs that are suitable fr maipulati. Oly a cmm parsig ifrastructure ca prduce AST structures that allw a rewrite egie ad cde geerati ifrastructure t fucti ver arbitrary dmai laguages ad cmbiatis f laguages. Custmers ca becme trasfrmati tl builders. There is a sigificat learig curve i buildig trasfrmati-based tls. A custmer seekig a sigle tl ca save mey by lettig trasfrmati specialists build it. But trasfrmati methds are well-suited t a rage f sftware life cycle tasks, ad egieers ca be traied t build tls themselves ad icrprate the techlgy it their perati with great beefit ad cst savigs. 9. Related Wrk Surce-t-surce prgram trasfrmatis were rigially cceived as a methd f prgram geerati i the 1970s [2], ad the techlgy has bee develpig sice [10, 11]. The idea that trasfrmatis culd be used fr sftware maiteace ad evluti by chagig a specificati ad re-sythesizig was suggested i the early 80s [4]. Prtig sftware ad carryig ut chages were suggested ad demstrated i the late 80s [1, 9]. Thery abut hw t mdify prgrams trasfrmatially usig previusly captured desig ifrmati was suggested i 1990[3]. Refie [6,14] was a grudbreakig sftware trasfrmati egie which was used as a basis fr sme blackbx cmmercial autmated migrati prjects. But prgram trasfrmati as a serius tl fr sftware evluti is largely urealized i practice.

10 Mechaical refactrig [13] was prpsed i 1990 as a techique fr restructurig prgrams ad was recetly ppularized [7] as a methdlgy with suggestis fr tl supprt. Tls fr refactrig SmallTalk [15] ad Java have started t appear, ad sme experimetal wrk has bee de i refactrig C++ [18]. The better Java tls [19,20] d sme sphisticated refactrigs such as ExtractMethd; thers i the market require sme maual validati f the steps. 10. Future Directis The PRiSm r CORBA cmpet techlgies impse cmputatial verhead as service requests are ruted thrugh several ew layers f cmpet cmmuicati prtcl. Essetially, the extra layers exist t prvide separati f ccer i desig ad cdig ad t prvide plug-ad-play capability at cfigurati time. Mechaized static partial evaluati culd relieve this verhead. With sematic awareess f the cmpet wirig, a trasfrmati tl culd be develped t statically evaluate the varius cmmuicati idirectis, sparig ru-time verhead. I this highly perfrmace-sesitive evirmet, the effrt culd be well justified. Sematics-based aalysis ca als be applied t deeper partial evaluati f the cde resultig frm the dyamic assembly f cmpets it a flight cfigurati. Fr example, cde that supprts cfiguratis that are t i play ad cditials that dyamically test fr thse cfiguratis ca be elimiated. Idirectly called prcedures ca be ilied, avidig idirecti ad call verhead. Cmbiig autmated aalysis ad cde trasfrmati at build time shuld ehace perfrmace. 11. Ackwledgemets We thak ur cllabratr i this effrt, the Beig Cmpay, t the DARPA PCES prgram fr fudig, ad t Lrraie Bier fr dcumet preparati. 12. Refereces [1] G. Arag, I. Baxter, C. Pidge, P. Freema, "TMM: Sftware Maiteace by Trasfrmati", IEEE Sftware 3(3), May 1986, pp [2] R. M. Balzer, N. M. Gldma, ad D. S. Wile, "O the Trasfrmatial Implemetati Apprach t Prgrammig", Prceedig, 2d Iteratial Cferece Sftware Egieerig, Oct. 1976, pp [3] I. Baxter, Trasfrmatial Maiteace by Reuse f Desig Histries, Ph.D. Thesis, Ifrmati ad Cmputer Sciece Departmet, Uiversity f Califria at Irvie, Nv. 1990, TR [4] I. Baxter, "Desig Maiteace Systems", Cmmuicatis f the ACM 35(4), 1992, ACM. [5] I. D. Baxter, C. Pidge., ad M. Mehlich, "DMS: Prgram Trasfrmatis fr Practical Scalable Sftware Evluti". Prceedigs f the 26th Iteratial Cferece Sftware Egieerig, [6] S. Burs, G. B. Ktik, ad L. Z. Marksia, "A Prgram Trasfrmati Apprach t Autmatig Sftware Reegieerig", Prceedigs f the 14th Aual Iteratial Cmputer Sftware & Applicatis Cferece (COMPSAC 90), IEEE Publishers, [7] M. Fwler, Refactrig: Imprvig the Desig f Existig Cde, Addis Wesley [8] V. Giddig, B. Beckwith, "Real-time CORBA Tutrial", OMG's Wrkshp Distributed Object Cmputig fr Real-Time ad Embedded Systems 2003, [9] W. L. Jhs ad M. S. Feather, "Usig Evluti Trasfrms t Cstruct Specificatis", M. Lwry ad R. McCartey (eds.), Autmatig Sftware Desig, AAAI Press, [10] E. Kat, F. Daube, E. MacGregr, ad J. Wald, "Scietific Prgrammig by Autmated Sythesis", i: Michael R. Lwery ad Rbert D. McCartey (eds.), Autmatig Sftware Desig, MIT Press, [11] J. Neighbrs, "Drac: A Methd fr Egieerig Reusable Sftware Systems", i: T. Biggerstaff ad A. Perlis (eds.), Sftware Reusability, ACM Press [12] W.F. Opdyke, Refactrig Object-Orieted Framewrks, PhD Thesis, Uiversity f Illiis at Urbaa-Champaig. Als available as Techical Reprt UIUCDCS-R , Departmet f Cmputer Sciece, Uiversity f Illiis at Urbaa-Champaig. [13] PARLANSE Referece Maual, Sematic Desigs, [14] Reasig Systems, Pal Alt, CA, "Refie Laguage Tls", [15] D. Rberts, J. Brat, R. Jhs ad W. Opdyke, "A Autmated Refactrig Tl", Prceedigs f ICAST '96: 12th Iteratial Cferece Advaced Sciece ad Techlgy, Chicag, Illiis. April, [16] Sematic Desigs, Ic., [17] D. C. Sharp, "Reducig Aviics Sftware Cst Thrugh Cmpet Based Prduct Lie Develpmet", Prceedigs f the 1998 Sftware Techlgy Cferece. [18] L. Tkuda ad D. Batry, "Evlvig Object Orieted Desigs with Refactrig", Prceedigs f the Cferece Autmated Sftware Egieerig, IEEE, [19] IDEA refactrig tl fr Java. [20] Jfactr refactrig tl fr Java.