Virtual Machine (Part I)

Transcription

1 Hrvrd University CS Fll 2, Shimon Schocken Virtul Mchine (Prt I) Elements of Computing Systems Virtul Mchine I (Ch. 7) Motivtion clss clss Min Min sttic sttic x; x; function function void void min() min() // // Input Input nd nd multiply multiply 2 2 numers numers vr vr,, ; ; Keyord.redInt( Enter Keyord.redInt( Enter numer ); numer ); Keyord.redInt( Enter Keyord.redInt( Enter numer ); numer ); x x mult(,); mult(,); return; return; // // Multiplies Multiplies two two numers. numers. function function mult( mult( x, x, y) y) vr vr,, ; ; ; ; y; y; while while not( not( ) ) + + x; x; ; ; return return ; ; Ultimte gol: Compile strct progrms o executle code. Compiler M M (LOOP) (LOOP) D;JGT D;JGT MD+M MD+M ;JMP ;JMP ;JMP ;JMP Elements of Computing Systems 2 Virtul Mchine I (Ch. 7)

2 Compiltion models direct compiltion: lnguge lnguge 2 lnguge n 2-tier compiltion: lnguge lnguge 2 lnguge n ermedite lnguge hrdwre pltform hrdwre pltform 2. requires n m trnsltors hrdwre pltform m hrdwre pltform hrdwre pltform 2 requires n + m trnsltors hrdwre pltform m Two-tier compiltion: First compiltion stge depends only on the detils of the source lnguge Second compiltion stge depends only on the detils of the trget lnguge. Elements of Computing Systems 3 Virtul Mchine I (Ch. 7) The Hck/Jck pltform VM implementtion over CISC pltforms The ermedite code: Some lnguge Some compiler VM imp. over RISC pltforms Some Other lnguge Some Other compiler Intermedite code VM emultor Jck lnguge Jck compiler VM imp. over the Hck pltform The erfce etween the 2 compiltion stges Must e sufficiently strct to support mny (high-level lnguge, mchine lnguge) pirs Defines stnd-lone lnguge of n strct mchine Cn e modeled s the lnguge of n strct virtul mchine (VM). CISC mchine lnguge RISC mchine lnguge written in high-level lnguge Hck mchine lnguge CISC mchine RISC mchine other digitl pltforms, ech equipped with its VM implementtion Any computer Hck computer Elements of Computing Systems 4 Virtul Mchine I (Ch. 7)

3 A stck mchine - sed VM Stck push 8 Stck (efore) (fter) Stck pop Stck Mor dt structure Elegnt nd powerful Implementtion options. Elements of Computing Systems Virtul Mchine I (Ch. 7) Stck rithmetic 7 4 dd 7 9 Typicl opertion: Pops two rguments from the stck Adds their vlue Pushes the onto the stck. Impct: the opernds re replced with the opertion s In generl: similr impct for ll rithmetic nd Boolen opertions. Elements of Computing Systems 6 Virtul Mchine I (Ch. 7)

4 Evlution of rithmetic expressions // d(2-x)*(y+) push 2 push x su push y push dd mult pop d x y 9 Stck push 2 2 push x 2 su push y 9 push dd mult -42 pop d Stck x y 9 d -42 Elements of Computing Systems 7 Virtul Mchine I (Ch. 7) Evlution of Boolen expressions // if (x<7) or (y8) push x push 7 lt push y push 8 eq or x 2 y 8 Stck 2 2 push x push 7 lt 7 flse flse flse push y 8 push 8 eq 8 8 flse true or true Elements of Computing Systems 8 Virtul Mchine I (Ch. 7)

5 VM specifiction: dt types Our VM fetures single 6-it dt type tht cn e used s: Integer Boolen Poer Elements of Computing Systems 9 Virtul Mchine I (Ch. 7) VM specifiction: commnds Arithmetic // Boolen commnds dd dd su su neg neg eq eq This lecture gt gt lt lt nd nd or or not not ccess commnds Progrm flow flow commnds lel (declrtion) (declrtion) goto goto (lel) (lel) if-goto (lel) (lel) Next lecture Function clling commnds function (declrtion) (declrtion) cll cll ( ( function) function) return (from (from function) function) pop pop segment i push pushsegment i Elements of Computing Systems Virtul Mchine I (Ch. 7)

6 Arithmetic nd Boolen commnds Elements of Computing Systems Virtul Mchine I (Ch. 7) ccess commnds (So fr, pop/push commnds cted on glol memory. This ws conceptul simplifiction ) segments rgument: stores the current function s rguments locl: stores the function s locl vriles sttic: stores glol vriles, shred y ll functions in the sme.vm file constnt: pseudo segment holding ll the constnts in the rnge this, tht: generl-purpose segments; cn e mde to correspond to different res in the hep poer: used to lign this nd tht temp: fixed 8-entry segment tht holds temporry vriles for generl use; Shred y ll VM functions in the progrm. ccess commnds formt: pop pop memorysegment i push push memorysegment i Elements of Computing Systems 2 Virtul Mchine I (Ch. 7)

7 Motivtion VM progrmming exmples: Arithmetic tsk Arry hndling tsk Oect hndling tsk (These exmple don t elong to this lecture, nd re given here for motivtion only.) Elements of Computing Systems 3 Virtul Mchine I (Ch. 7) Arithmetic exmple High-level code function function mult(x,y) mult(x,y),, ; ; ; ; y; y; while while ~() ~() +x; -; -; return return ; ; Just fter mult(7,3) is entered: Stck rgument locl 7 Just fter mult(7,3) returns: Stck 2 3 x y sum Pseudo VM code function function mult(x,y) mult(x,y) push push pop pop push push y pop pop lel lel loop loop push push push push eq eq if-goto if-goto end end push push push push x dd dd pop pop push push push push su su pop pop goto goto loop loop lel lel end end push push return return VM code function function mult mult 2 push push constnt constnt pop pop locl locl push push rgument rgument pop pop locl locl lel lel loop loop push push locl locl push push constnt constnt eq eq if-goto if-goto end end push push locl locl push push rgument rgument dd dd pop pop locl locl push push locl locl push push constnt constnt su su pop pop locl locl goto goto loop loop lel lel end end push push locl locl return return Elements of Computing Systems 4 Virtul Mchine I (Ch. 7)

8 Arry hndling exmple r rry High-level progrm view RAM view 7 3 following r compiltion (Actul RAM loctions of progrm vriles re run-time dependent, nd thus the ddresses shown here re ritrry exmples.) r rry /* /* Assume Assume tht tht r r is is the the first first locl locl vrile vrile declred declred in in the the high-level progrm. progrm. The The code code elow elow implements r[2]9, or or *(r+2)9. */ */ // // Get Get r's r's se se ddress: ddress: push push locl locl push push constnt constnt 2 dd dd // // Set Set tht s tht s se se to to (r+2): (r+2): pop pop poer poer push push constnt constnt 9 9 // // *(r+2)9: pop pop tht tht Virtul memory segments Just efore the r[2]9 opertion: Virtul memory segments Just fter the r[2]9 opertion: locl poer tht locl poer tht (tht is now lligned with RAM[437]) Elements of Computing Systems Virtul Mchine I (Ch. 7) Oect hndling exmple oect High level progrm view x: y: rdius: color: following compiltion (Actul RAM loctions of progrm vriles re run-time dependent, nd thus the ddresses shown here re ritrry exmples.) RAM view oect /* /* Assume Assume tht tht nd nd r were were pssed pssed to to the the function function s s its its first first two two rguments. The The following following code code implements the the opertion opertion.rdiusr. */ */ // // Get Get 's 's se se ddress: ddress: push push rgument rgument // // Po Po the the this this seg. seg. to to : : pop pop poer poer // // Get Get r's r's vlue vlue push push rgument rgument // // Set Set 's 's third third field field to to r: r: pop pop this this 2 Virtul memory segments ust efore the opertion.rdius7: rgument poer this 32 7 Virtul memory segments ust fter the opertion.rdius7: rgument poer this (this is now lligned with RAM[32]) Elements of Computing Systems 6 Virtul Mchine I (Ch. 7)

9 The VM lnguge summry Arithmetic / Boolen commnds (dd, su, eq, ) commnds (pop, push) Progrm flow commnds (lel, goto, if-goto) Function clling commnds (function, cll, return) This lecture Next lecture VM implementtion options: Softwre-sed (emultion) Hrdwre-sed (e.g. Hck) Fmous VM implementtions: JRE (runs ytecode) CLR (runs IL progrms) Elements of Computing Systems 7 Virtul Mchine I (Ch. 7) VM implementtion on the Hck pltform TEMP LCL ARG THIS THAT locl,rgument,this,tht: mpped directly on the host RAM. The se ddresses of these segments re kept in the registers lcl,arg,this,that. Access to the i-th entry of segment s in ccessing the (se + i) word in the RAM 3 Generl purpose 4 6 Sttics sttic: sttic vrile numer in VM file f is represented s the ssemly lnguge symol f Stck constnt: truly virtul segment. Access to constnt i s in supplying the constnt i 248 Hep poer,temp: see the ook. Elements of Computing Systems 8 Virtul Mchine I (Ch. 7)

10 Prser module (proposed design) Prser: Hndles the prsing of single.vm file, nd encpsultes ccess to the input code. It reds VM commnds, prses them, nd provides convenient ccess to their components. In ddition, it removes ll white spce nd comments. Routine Constructor Arguments Input file / strem Returns Function Opens the input file/strem nd gets redy to prse it. hsmorecommnds oolen Are there more commnds in the input? dvnce Reds the next commnd from the input nd mkes it the current commnd. Should e clled only if hsmorecommnds() is true. Initilly there is no current commnd. commndtype C_ARITHMETIC, C_PUSH, C_POP, C_LABEL, C_GOTO, C_IF, C_FUNCTION, C_RETURN, C_CALL Returns the type of the current VM commnd. C_ARITHMETIC is returned for ll the rithmetic commnds. rg string Returns the first rgument of the current commnd. In the cse of C_ARITHMETIC, the commnd itself (dd, su, etc.) is returned. Should not e clled if the current commnd is C_RETURN. rg2 Returns the second rgument of the current commnd. Should e clled only if the current commnd is C_PUSH, C_POP, C_FUNCTION, or C_CALL. Elements of Computing Systems 9 Virtul Mchine I (Ch. 7) CodeWriter module (proposed design) CodeWriter: Trnsltes VM commnds o Hck ssemly code. Routine Arguments Returns Function Constructor Output file / strem Opens the output file/strem nd gets redy to write o it. setfilenme filenme (string) Informs the code writer tht the trnsltion of new VM file is strted. writearithmetic commnd (string) Writes the ssemly code tht is the trnsltion of the given rithmetic commnd. WritePushPop Commnd (C_PUSH or C_POP), segment (string), Writes the ssemly code tht is the trnsltion of the given commnd, where commnd is either C_PUSH or C_POP. index () Close Closes the output file. Comment: More routines will e dded to this module in chpter 8. Elements of Computing Systems 2 Virtul Mchine I (Ch. 7)

11 The VM emultor Elements of Computing Systems 2 Virtul Mchine I (Ch. 7)