Virtual Machine I: Stack Arithmetic

Transcription

1 Virtul Mchine I: Stck Arithmetic Building Modern Computer From First Principles Elements of Computing Systems, Nisn & Schocken, MIT Press, Chpter 7: Virtul Mchine I: Stck Arithmetic slide 1

2 Where we re t: Humn Thought Abstrct design Chpters 9, 12 bstrct interfce H.L. Lnguge & Operting Sys. Compiler Chpters bstrct interfce Virtul Mchine Softwre hierrchy VM Trnsltor Chpters 7-8 bstrct interfce Assembly Lnguge Assembler Chpter 6 bstrct interfce Mchine Lnguge Computer Architecture Chpters 4-5 Hrdwre hierrchy bstrct interfce Hrdwre Pltform Gte Logic Chpters 1-3 bstrct interfce Chips & Logic Gtes Electricl Engineering Physics Elements of Computing Systems, Nisn & Schocken, MIT Press, Chpter 7: Virtul Mchine I: Stck Arithmetic slide 2

3 Motivtion clss clss Min Min { { sttic sttic int int x; x; function function void void min() min() { { // // Input Input nd nd multiply multiply 2 2 numbers numbers vr vr int int,, b, b, x; x; Keybord.redInt( Enter Keybord.redInt( Enter number ); number ); b b Keybord.redInt( Enter Keybord.redInt( Enter number ); number ); x x mult(,b); mult(,b); return; return; } } } } // // Multiplies Multiplies two two numbers. numbers. function function int int mult(int mult(int x, x, int int y) y) { { vr vr int int result, result, j; j; result result 0; 0; j j y; y; while while not(j not(j 0) 0) { { result result result result + + x; x; j j j j 1; 1; } } return return result; result; } } } } Ultimte gol: Trnslte highlevel progrms into executble M0 M ;JMP 0;JMP 0;JMP 0;JMP Elements of Computing Systems, Nisn & Schocken, MIT Press, Chpter 7: Virtul Mchine I: Stck Arithmetic slide 3

4 Compiltion models direct compiltion: lnguge 1 lnguge 2 lnguge n 2-tier compiltion: lnguge 1 lnguge 2 lnguge n intermedite lnguge hrdwre pltform 1 hrdwre pltform 2. requires n m trnsltors hrdwre pltform m hrdwre pltform 1 hrdwre pltform 2 requires n + m trnsltors hrdwre pltform m Two-tier compiltion: 1 st compiltion stge depends only on the detils of the source lnguge 2 nd compiltion stge depends only on the detils of the trget pltform. Elements of Computing Systems, Nisn & Schocken, MIT Press, Chpter 7: Virtul Mchine I: Stck Arithmetic slide 4

5 The big picture VM implementtion over CISC pltforms 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 intermedite code: The interfce between the 2 compiltion stges Must be sufficiently generl to support mny <HLL, ML> pirs Cn be modeled s the lnguge of n bstrct virtul mchine (VM) Cn be implemented in severl different wys. 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 own VM implementtion Any computer Hck computer Elements of Computing Systems, Nisn & Schocken, MIT Press, Chpter 7: Virtul Mchine I: Stck Arithmetic slide 5

6 Focus of this lecture: Some lnguge Some Other lnguge Jck lnguge Some compiler Some Other compiler Jck compiler Chpters 9-13 VM lnguge VM implementtion over CISC pltforms VM imp. over RISC pltforms VM emultor VM imp. over the Hck pltform Chpters 7-8 CISC mchine lnguge RISC mchine lnguge written in high-level lnguge Hck mchine lnguge Chpters 1-6 CISC mchine RISC mchine other digitl pltforms, ech equipped with its VM implementtion Any computer Hck computer Elements of Computing Systems, Nisn & Schocken, MIT Press, Chpter 7: Virtul Mchine I: Stck Arithmetic slide 6

7 Lecture pln Gol: Specify nd implement VM model nd lnguge: Arithmetic // Boolen commnds dd dd sub sub neg neg eq eq gt gt This lecture lt lt nd nd or or not not Memory ccess commnds pop pop x (pop (pop into into x, x, which which is is vrible) vrible) push pushy (y (y being being vrible vrible or or constnt) constnt) Progrm flow flow commnds lbel (declrtion) (declrtion) goto goto (lbel) (lbel) if-goto (lbel) (lbel) Next lecture Function clling commnds function (declrtion) (declrtion) cll cll ( ( function) function) return (from (from function) function) Method: () specify the bstrction (model s constructs nd commnds) (b) propose how to implement it over the Hck pltform. Elements of Computing Systems, Nisn & Schocken, MIT Press, Chpter 7: Virtul Mchine I: Stck Arithmetic slide 7

8 The VM model nd lnguge Perspective: From here till the end of this nd the next lecture we describe the VM model used in the Hck-Jck pltform Other VM models (like JVM/JRE nd IL/CLR) re similr in spirit but different in scope nd detils. progrmmers re cretors of universes for which they lone re responsible. Universes of virtully unlimited complexity cn be creted in the form of computer progrms. (Joseph Weizenbum) The VM model + lnguge re n exmple of one such universe View I: the VM is mchine tht mkes sense in its own right View II: the VM is convenient in-between representtion of computer progrm: n interim sttion between the high-level code nd the mchine level code. Elements of Computing Systems, Nisn & Schocken, MIT Press, Chpter 7: Virtul Mchine I: Stck Arithmetic slide 8

9 Our VM is stck-oriented mchine dd 17 9 Our VM fetures single 16-bit dt type tht cn be used s: Integer Boolen Pointer Typicl opertion: Pops topmost vlues x,y from the stck Computes the vlue of some function f(x,y) Pushes the result onto the stck (Unry opertions re similr, using x nd f(x) insted) Impct: the opernds re replced with the opertion s result In generl: ll rithmetic nd Boolen opertions re implemented similrly. Elements of Computing Systems, Nisn & Schocken, MIT Press, Chpter 7: Virtul Mchine I: Stck Arithmetic slide 9

10 Memory ccess (first pproximtion) Stck Memory 17 push b b Stck b Memory (before) (fter) Elements of Computing Systems, Nisn & Schocken, MIT Press, Chpter 7: Virtul Mchine I: Stck Arithmetic slide 10

11 Memory ccess (first pproximtion) Stck Memory 17 push b b Stck b Memory (before) (fter) Stck b Memory pop Stck b Memory Clssicl dt structure Elegnt nd powerful Severl hw/sw implementtion options. Elements of Computing Systems, Nisn & Schocken, MIT Press, Chpter 7: Virtul Mchine I: Stck Arithmetic slide 11

12 Evlution of rithmetic expressions // d(2-x)*(y+5) push 2 push x sub push y push 5 dd mult pop d x 5 y Memory 9 Stck push 2 2 push x 2 sub push y 9 push 5 dd mult pop d Stck x 5 y Memory 9 d -42 Elements of Computing Systems, Nisn & Schocken, MIT Press, Chpter 7: Virtul Mchine I: Stck Arithmetic slide 12

13 Evlution of Boolen expressions // if (x<7) or (y8) push x push 7 lt push y push 8 eq or x 12 y Memory 8 Stck push x push 7 7 lt flse flse flse push y 8 push 8 eq 8 8 flse true or true Elements of Computing Systems, Nisn & Schocken, MIT Press, Chpter 7: Virtul Mchine I: Stck Arithmetic slide 13

14 Arithmetic nd Boolen commnds (wrp-up) Elements of Computing Systems, Nisn & Schocken, MIT Press, Chpter 7: Virtul Mchine I: Stck Arithmetic slide 14

15 Memory segments Modern progrmming lnguges normlly feture the following vrible kinds: Clss level Sttic vribles Privte vribles (AKA object vribles / fields / properties ) Method level: Locl vribles Argument vribles The VM bstrction must support (t lest) these vrible kinds. In our VM model, these vribles re stored in virtul memory segments Specificlly, our VM model consists of 8 memory segments: sttic, this, locl, rgument As well s: tht, constnt, pointer, nd temp. Elements of Computing Systems, Nisn & Schocken, MIT Press, Chpter 7: Virtul Mchine I: Stck Arithmetic slide 15

16 Memory segments nd memory ccess commnds So we hve 8 virtul memory segments: sttic, this, locl, rgument, tht, constnt, pointer, temp But, t the VM level, there is no need to differentite mong the different roles of these segments As fr s VM progrmming commnds go, segment is segment is segment; to ccess prticulr segment entry, use the syntx: Memory ccess commnd formt: pop pop segment ii push push segment ii These commnds re used insted of pop x nd push y, s shown in previous slides, which ws conceptul simplifiction The mening of the different eight segments will become importnt when we ll tlk bout the compiler. Elements of Computing Systems, Nisn & Schocken, MIT Press, Chpter 7: Virtul Mchine I: Stck Arithmetic slide 16

17 VM progrmming VM progrms re normlly written by compilers, not by humns But, for humn to write or optimize compiler, the humn must first understnd the spirit of VM progrmming So, here is n exmple. Elements of Computing Systems, Nisn & Schocken, MIT Press, Chpter 7: Virtul Mchine I: Stck Arithmetic slide 17

18 Arithmetic exmple High-level code function function mult mult (x,y) (x,y) { int int result, result, j; j; result result 0; 0; j y; y; while while ~(j ~(j 0) 0) { result result result result + x; x; j j - 1; 1; } return return result; result; } Just fter mult(7,3) is entered: Stck rgument locl 0 7 Just fter mult(7,3) returns: Stck x 0 y 1 0 sum 0 j VM code (first pprox.) function function mult(x,y) mult(x,y) push push 0 pop pop result result push push y pop pop j lbel lbel loop loop push push j push push 0 eq eq if-goto if-goto end end push push result result push push x dd dd pop pop result result push push j push push 1 sub sub pop pop j goto goto loop loop lbel lbel end end push push result result return return VM code function function mult mult 2 push push constnt constnt 0 pop pop locl locl 0 push push rgument rgument 1 pop pop locl locl 1 lbel lbel loop loop push push locl locl 1 push push constnt constnt 0 eq eq if-goto if-goto end end push push locl locl 0 push push rgument rgument 0 dd dd pop pop locl locl 0 push push locl locl 1 push push constnt constnt 1 sub sub pop pop locl locl 1 goto goto loop loop lbel lbel end end push push locl locl 0 return return Elements of Computing Systems, Nisn & Schocken, MIT Press, Chpter 7: Virtul Mchine I: Stck Arithmetic slide 18

19 Lecture pln Gol: Specify nd implement VM model nd lnguge Arithmetic // Boolen commnds dd dd sub sub neg neg eq eq gt gt This lecture lt lt nd nd or or not not Memory ccess commnds pop pop segment i push pushsegment i Progrm flow flow commnds lbel (declrtion) (declrtion) goto goto (lbel) (lbel) if-goto (lbel) (lbel) Next lecture Function clling commnds function (declrtion) (declrtion) cll cll ( ( function) function) return (from (from function) function) Method: () specify the bstrction (model s constructs nd commnds) (b) propose how to implement it over the Hck pltform. Elements of Computing Systems, Nisn & Schocken, MIT Press, Chpter 7: Virtul Mchine I: Stck Arithmetic slide 19

20 Implementtion VM implementtion options: Softwre-bsed (emulte the VM using, sy, Jv) Trnsltor-bsed (trnslte VM progrms into, sy, the Hck lnguge) Hrdwre-bsed (relize the VM using dedicted memory nd registers) Well-known trnsltor-bsed implementtions: JVM (runs bytecode progrms in the Jv pltform) CLR (runs IL progrms in the.net pltform). Elements of Computing Systems, Nisn & Schocken, MIT Press, Chpter 7: Virtul Mchine I: Stck Arithmetic slide 20

21 Our VM emultor (prt of the course softwre suite) Elements of Computing Systems, Nisn & Schocken, MIT Press, Chpter 7: Virtul Mchine I: Stck Arithmetic slide 21

22 Stndrd VM implementtion on the Hck pltform TEMP Generl purpose LCL ARG THIS THAT Host RAM Sttics Stck Hep The chllenge: (i) mp the VM constructs on the host RAM, nd (ii) given this mpping, figure out how to implement ech VM commnd using ssembly commnds tht operte on the RAM locl,rgument,this,tht: mpped on the hep. The bse ddresses of these segments re kept in LCL,ARG,THIS,THAT. Access to the i-th entry of segment is implemented by ccessing the segment s (bse + i) word in the RAM sttic: sttic vrible number j in VM file f is implemented by the ssembly lnguge symbol f.j (nd recll tht the ssembler mps such symbols to the RAM strting from ddress 16) constnt: truly virtul segment: Access to constnt i is implemented by supplying the constnt i pointer: used to lign this nd tht with memory blocks on the hep Exercise: given the bove gme rules, write the Hck commnds tht implement, sy, push constnt 5 nd pop locl 2. Elements of Computing Systems, Nisn & Schocken, MIT Press, Chpter 7: Virtul Mchine I: Stck Arithmetic slide 22

23 Proposed VM trnsltor implementtion: Prser module 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 Arguments Returns Function Constructor Input file / strem -- Opens the input file/strem nd gets redy to prse it. hsmorecommnds -- boolen Are there more commnds in the input? dvnce Reds the next commnd from the input nd mkes it the current commnd. Should be 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. rg1 -- string rg2 -- int Returns the first rgument of the current commnd. In the cse of C_ARITHMETIC, the commnd itself (dd, sub, etc.) is returned. Should not be clled if the current commnd is C_RETURN. Returns the second rgument of the current commnd. Should be clled only if the current commnd is C_PUSH, C_POP, C_FUNCTION, or C_CALL. Elements of Computing Systems, Nisn & Schocken, MIT Press, Chpter 7: Virtul Mchine I: Stck Arithmetic slide 23

24 Proposed VM trnsltor implementtion: CodeWriter module CodeWriter: Trnsltes VM commnds into Hck ssembly code. Routine Arguments Returns Function Constructor Output file / strem -- Opens the output file/strem nd gets redy to write into it. setfilenme filenme (string) -- Informs the code writer tht the trnsltion of new VM file is strted. writearithmetic commnd (string) -- Writes the ssembly code tht is the trnsltion of the given rithmetic commnd. WritePushPop Commnd (C_PUSH or C_POP), segment (string), index (int) -- Writes the ssembly code tht is the trnsltion of the given commnd, where commnd is either C_PUSH or C_POP. Close Closes the output file. Comment: More routines will be dded to this module in chpter 8. Elements of Computing Systems, Nisn & Schocken, MIT Press, Chpter 7: Virtul Mchine I: Stck Arithmetic slide 24

25 Perspective Some lnguge Some compiler Some Other lnguge Some Other compiler Jck compiler VM lnguge In this lecture we begn the process of building compiler VM implementtion over CISC pltforms VM imp. over RISC pltforms CISC RISC mchine mchine lnguge lnguge VM emultor Trnsltor written in high-level lnguge Hck Modern compiler rchitecture: Front-end (trnsltes from high level lnguge to VM lnguge) Bck-end (trnsltes from the VM lnguge to the mchine lnguge of some trget hrdwre pltform) Brief history of virtul mchines: 1970 s: p-code 1990 s: Jv s JVM 2000 s: Microsoft.NET A full blown VM implementtion typiclly includes common softwre librry (cn be viewed s mini, portble OS). We will build such mini OS lter in the course. Elements of Computing Systems, Nisn & Schocken, MIT Press, Chpter 7: Virtul Mchine I: Stck Arithmetic slide 25

26 The rod hed Tsks: Compe the VM specifiction nd implementtion (chpters 7,8) Introduce Jck, high-level progrmming lnguge (chpter 9) Build compiler for it (chpters 10,11) Finlly, build mini-os, i.e. run-time librry (chpter 12). Conceptully similr to: JVM Jv Jv compiler JRE And to: CLR C# C# compiler.net bse clss librry Elements of Computing Systems, Nisn & Schocken, MIT Press, Chpter 7: Virtul Mchine I: Stck Arithmetic slide 26