Procedure Abstraction

Transcription

1 Compiler Design Procedure Absrcion Hwnsoo Hn

2 Conrol Absrcion Procedures hve well-defined conrol-flow The Algol-60 procedure cll Invoked cll sie, wih some se of cul prmeers Conrol reurns o cll sie, immediely fer invocion s = p(10,,u); in p(,b,c) in, b, c; { in d; d = q(c,b);... in q(x,y) in x,y; { reurn x + y; Mos lnguges llow recursion 2

3 Requiremen for Conrol Absrcion Implemening procedures wih his behvior Requires code o sve nd resore reurn ddress Mus mp cul prmeers o forml prmeers Mus cree sorge for locl vribles (mybe, for prmeers) p needs spce for d (mybe, for, b, & c) where does his spce go in recursive invocions? Mus preserve p s se while q execues recursion cuses he rel problem here Sregy: Cree unique locion for ech procedure civion Cn use sck of memory blocks o hold locl sorge nd reurn ddresses 3

4 Nme Spce Ech procedure crees is own nme spce Any nme (lmos) cn be declred loclly Locl nmes obscure idenicl non-locl nmes Locl nmes cnno be seen ouside he procedure Nesed procedures re inside by definiion We cll his se of rules & convenions lexicl scoping Exmples C hs globl, sic, locl, nd block scopes Blocks cn be nesed, procedures cnno Jv hs prive, proeced, public, pckge scopes Blocks cn be nesed, mehods cn be nesed 4

5 Lexicl Scopes Lexicl scoping Provides compile-ime mechnism o use sic coordine for ech vrible nme Simplifies rules for nming & resolves conflics Ech nme refers o is lexiclly closes declrion Keeping rck of ll he nmes A progrm poin, need o deermine which declrion of x is curren A run-ime, where cn x be found? (ddressbiliy) Lexiclly scoped symbol bles llow lexicl scoping 5

6 Exmple procedure p { in, b, c procedure q { in v, b, x, w procedure r { in y, z = x procedure s { in x,, v r() r() s() q() Which x? B0: { in, b, c B1: { in v, b, x, w B2: { in y, z = x B3: { in x,, v 6

7 Lexiclly-Scoped Symbol Tbles High-level ide Cree new ble for ech scope (hsh ble for ech scope) Chin hem ogeher for lookup s r x v x y z q v b x w p b c Shef of bles implemenion inser(v) my need o cree ble i lwys insers v curren level lookup(v) wlks chin of bles & reurns firs occurrence of nme v delee() hrows wy ble for curren level, if i is op ble in he chin If he compiler mus preserve he ble, ble cn be sored in file Individul bles cn be hsh bles 7

8 Where Do All Vribles Go? Auomic & Locl Keep hem in he procedure civion record or in regiser Auomic lifeime mches procedure s lifeime Sic Procedure scope sorge re ffixed wih procedure nme &_p.x File scope sorge re ffixed wih file nme Lifeime is enire execuion Globl One or more nmed globl d res Lifeime is enire execuion 8

9 Plcing Run-ime D Srucures Clssic Orgnizion C o d e S G l & o b i c l H e p 0 high Single Logicl Address Spce S c k Beer uilizion if sck & hep grow owrd ech oher Uses ddress spce, no lloced memory Code, sic, & globl d hve known size Use symbolic lbels, no numeric ddress, in he code Hep & sck boh grow & shrink over ime This is virul ddress spce 9

10 10 How Does This Relly Work? The Big Picure C o d e S G l & o b i c l H e p S c k C o d e S G l & o b i c l H e p S c k C o d e S G l & o b i c l H e p S c k Hrdwre s view Compiler s view OS s view Physicl ddress spce_ virul ddress spces 0 high C o d e S G l & o b i c l H e p S c k

11 Trnsling Locl Nmes How does he compiler represen specific insnce of x? Nme is rnsled ino sic coordine < level,offse > pir level is lexicl nesing level of he procedure offse is unique wihin h scope Subsequen code will use he sic coordine o genere ddresses nd references 11

12 Acivion Record Locl-D Are Spce for locl vlues & vribles (including spills) ARP Locl-D Are Cller s ARP Addressbiliy Reurn Address Cller s ARP Addressbiliy Reurn Address Reurn Vlue To resore cller s AR on reurn Help wih non-locl ccess Reurn Vlue Regiser-Sve Are Prmeers Regiser-Sve Are Prmeers Cller s AR Address o resume cller Spce for reurn vlue Cllee s AR Sved regiser conens Acivion record One AR per procedure ARP (civion record poiner) poins curren AR How does he compiler find he locl vribles? They re known offses from he AR poiner The sic coordine leds o lodai (bse + immedie offse) Level specifies n ARP, offse is he consn 12 Spce for prmeers o he curren rouine

13 Access Link - Addressbiliy Nesed lexicl scoping Lexiclly closes declrion Access links If no found in curren AR, wlk he chin of ccess links o serch nex closes one Globl disply Disply conins ARP of he mos recen procedure ech lexicl level Consn cos o ccess non-locls progrm min { in x; // def1 procedure r { = x; // which x? procedure s { in x; // def2 r(); = x; // which x? r(); s(); Globl Disply level0 level1 level2 level3 13

14 Access Link vs. Globl Disply Acivion Record vi Access Links ARP -4 level2 Cller s ARP Access Link level1 Cller s ARP Access Link level0 Cller s ARP Access Link Coordine Code <2, 24> lodai r rp, 24 => r2 <1, 12> lodai r rp, -4 => r1 lodai r1, 12 => r2 <0, 16> lodai r rp, -4 => r1 lodai r1, -4 => r1 lodai r1, 16 => r2 Acivion Record vi Globl Disply Globl Disply Cller s ARP Sved Pr level0 level1 Cller s ARP Sved Pr level2 level3 Cller s ARP Sved Pr Coordine Code <2, 24> lodai r rp, 24 => r2 <1, 12> lodi _disp => r1 lodai r1, 4 => r1 lodai r1, 12 => r2 <0, 16> lodi _disp => r1 lodai r1, 16 => r2 14

15 x86-64/linux Sck Frme Curren Sck Frme Argumen build: 7 h prmeer nd up Prmeers for funcion bou o cll Locl vribles If cn keep in regisers Sved regiser conex Old frme poiner (opionl) Cller Sck Frme Reurn ddress Pushed by cll insrucion Argumens for his cll Frme poiner %rbp (Opionl) Sck poiner %rsp Cller Frme Argumens (7 h +) Reurn Addr Old %rbp Sved Regisers + Locl Vribles Argumen Build (Opionl)

16 x86-64 Linux Regiser Usge #1 %rx Reurn vlue Also cller-sved Cn be modified by procedure %rdi,..., %r9 Argumens Also cller-sved Cn be modified by procedure %r10, %r11 Cller-sved Cn be modified by procedure Reurn vlue Argumens Cller-sved emporries %rx %rcx %rdx %rsi %rdi %r8 %r9 %r10 %r11 4 h rg 3 rd rg 2 nd rg 1 s rg 5 h rg 6 h rg

17 x86-64 Linux Regiser Usge #2 %rbx, %r12, %r13, %r14, %r15 Cllee-sved Cllee mus sve & resore %rbp Cllee-sved Cllee mus sve & resore My be used s frme poiner Cn mix & mch %rsp Specil form of cllee sve Cllee-sved Temporries Specil Resored o originl vlue upon exi from procedure %rbx %r12 %r13 %r14 %r15 %rbp %rsp

18 Communicing Beween Procedures Mos lnguges provide prmeer pssing mechnism Expression used cll sie becomes vrible in cllee Common binding mechnisms for prmeer pssing Cll-by-vlue psses copy of is vlue ime of cll Requires slo in he AR (or regiser) One nme (forml prmeer) refers o h vlue Cll-by-reference psses poiner o cul prmeer Requires slo in he AR (or regiser) Expression in cul prmeer is evlued nd sored in AR o pss is ddress Alises my exis oher nmes my refer o he sme locion Cll-by-resul psses he vlue of forml prmeer o he corresponding cul prmeer ime of reurn Argumens re used for resuls, no inpu prmeers 18

19 Procedure Linkges clling convenion Clling convenion Prmeer pssing Cll-by-reference, -vlue, -resul, -nme Sck clen-up Cller vs. cllee (cdecl vs. sdcll) How do procedure clls cully work? A compile ime, cllee my no be vilble for inspecion Differen clls my be in differen compilion unis Compiler my no know sysem code from user code All clls mus use he sme proocol Compiler mus use sndrd sequence of operions Enforces conrol & d bsrcions Divides responsibiliy beween cller & cllee Usully sysem-wide greemen (for ineroperbiliy) 19

20 Procedure Linkges Overview Sndrd procedure linkge procedure p prolog procedure q Procedure hs sndrd prolog sndrd epilog pre-cll pos-reurn epilog prolog epilog Ech cll involves pre-cll sequence pos-reurn sequence These re compleely predicble from he cll sie depend on he number & ype of he cul prmeers 20

21 Summry Views for procedure Conrol bsrcion, nme spce, inerfce Single ddress spce for ech progrm MMU nd OS provide virul ddress spce Compiler sees only single ddress spce Procedure linkge (clling convenion) Provides sysem-wide ineroperbiliy One civion record for ech procedure Cller nd cllee shre responsibiliy o preserve/build/resore execuion environmen 21