Listoflectures
IntroductionandFunctionalProgramming
ImperativeProgrammingandDataStructures
3 Environment
4 Evaluation
5 ObjectOrientedProgramming
6 Macrosanddecorators
7 VirtualMachinesandBytecode
8 GarbageCollectionandNativeCode
9 DistributedComputing
10LogicProgramming
11Summary
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2
TDDA69DataandProgramStructure
VirtualMachinesandBytecode
CyrilleBerger
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Howisaprograminterpreted?
Sourcecode
Learnwhatisavirtual
machine,bytecode
Learnhowtogenerate
thebytecodeandexecute
it
Parser
Parser
AbstractSyntaxTree
Treevisitor
Generator
Sourcecode
Bytecode
VirtualMachine
Assembler
Assembly
...
OperatingSystem
Lecturegoal
CPU
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Lecturecontent
VirtualMachines
Typesofvirtual/hardwaremachines
Bytecode
VirtualMachines
Simpleinstructionset
FromASTtoBytecode
Bytecodeinterpreter
Meta-circular
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LanguageVirtualMachine
WhatisaVirtualMachine?
AVirtualMachineisahardwareor
softwareemulationofarealor
hypotheticalcomputersystem
Asystemvirtualmachineemulatesa
completesystemandisintentedto
executeacompleteoperatingsystem
SourceCode
Compiler
ByteCode
Examples:VirtualBox,VMWare,Parallels...
Aprocess/languagevirtualmachineruns
asingleprograminasingleprocess
VirtualMachine
VirtualMachine
VirtualMachine
Windows
Linux
Mac
Examples:JVM,CPython,V8,Dalvik...
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8
BenefitsofVirtualMachines
NativeEnvironmentvsEmulatedEnvironment
OperatingSystem
Portability:VirtualMachinesare
compatiblewithvarioushardware
platformsandOperatingSystems
Isolation:VirtualMachinesare
isolatedfromeachother
Input/Output
NativeProgram
Hardware
Libraries
VirtualMachine
OperatingSystem
Emulated
HardwareInterface
Hardware
Bindings
Libraries
Emulated
Input/Output
EmulatedProgram
Forrunningincompatibleapplicationsconcurrently
Input/Output
Encapsulation:computationis
seperatedfromtheoperatingsystem
Beneficialforsecurity
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Typesofvirtual/hardwaremachines
Typesofvirtual/hardwaremachines
Register
Stack
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StackMachine:Formaldefinition
RegisterMachine:Formaldefinition
A(in)finitesetofregisters,whichholdsa
singlenon-negativeinteger
Aninstructionset,whichdefinesthe
operationonregisters
An(almost)infinitestack,whichholds
integers
Aninstructionset,whichdefinesthe
operationonthestack
Arithmetic,control,input/output...
Arithmeticoperationsarealwaysappliedonthetoptwo
registersandtheresultsisstoredinthetop
Astateregister,whichholdsthecurrent
instructionanditsindex
Sequentiallistoflabeledinstructions
whichdefinestheprogramtobeexecuted
Astateregister,whichholdsthecurrent
instructionanditsindex
Sequentiallistoflabeledinstructions
whichdefinestheprogramtobeexecuted
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VirtualMachinesforDynamicTyping
StackMachinesvsRegisterMachines
Remember:
StackMachinesneedmorecompactcode
Arithmeticinstructionaresmaller
Withstatictyping,typesarecheckedduring
compilation
Withdyamictyping,typesarecheckedduring
execution
StackMachineshavesimplercompiler,
interpretersandaminimalprocessorstate
StackMachineshaveaperformance
disadvantages
Implication
Morememoryreferences,lesscachingoftemporaries
Highercostoffactoringoutcommonsubexpressions
Stack/Registerscontainspointertoobjects
Functioncallconvention
Ithastobestoredasatemporaryvariable
Mostcommonhardwareareregistermachines
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Bytecode
Bytecode
Foravirtualstack
Instructionset
Generatethe
Interpretingthebytecode
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Stackmanagment
PUSH
Simpleinstructionset
Pushtheconstantonthestack
POP[number]
Popacertainnumbersofvariablesfromthe
stack
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Arithmeticoperators
Variables
ADD,
LOAD
Poptwoargumentsonthestack
Pushtheresult
Pushthevalueofvariable
DCL
Declarethevariable
STORE[varname]
Getthevalue,storetheresultandpushthe
value
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Jumps
Functions
JMP
CALL[arguments]
Jumptoexecuteinstructionatthegivenindex
Popthefunctionobjectandcallitwiththe
givennumberofarguments
IFJMP
RET
Popthevalueandiftruejumpto[idx]
Return
Buthowtoknowwheretoreturn?
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Objects
LOAD_MEMBER
Poptheobjectandpushthevalueofvariable
STORE_MEMBER
FromASTtoBytecode
Poptheobjectandvalueandstoreitandpush
thevalue
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FromASTtoBytecode
Arithmeticoperation
Withatree
Itcantakeseveral
1+2
a-2
var
a=1
vara=
a
a=b*c
a.b=c
Findthevariables
Computethejumps
Generatethecode
Therealchallengeistomap
highlevellanguageto
instructions
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Functions
Controls
func(1)
func(1,2)
console.log('Helloworld!')
functionfunc(a,b){returna+b;
}
if(a){console.log('test')}
if(a){console.log('hello')}
else{console.log('world')}
vara=10;
while(a){a-=1;}
for(vara=0;a<10;a+=1)
{console.log(a);}
for(vara=0;a<10;a+=1)
{console.log(a);if(a+b){break;}}
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Componentsofbytecodeinterpreter
Verifier
Bytecodeinterpreter
Bytecodemaycomefrombuggycompileror
malicioussource
Dynamiccheckingoftypes,arraybounds,
functionarguments...
Instructionexecuter
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Verification
Bytecodeinterpreter
Verifiercheckscorrectnessof
bytecode
Standardvirtualmachine
interpretsinstructions
Everyinstructionmusthaveavalidoperation
code
Everyinstructionmusthavevalidparameters
Everybranchinstructionmustbranchtothe
startofsomeotherinstruction,notmiddleof
instruction
Performrun-timecheckssuchasarraybounds
andtypesandfunctionarguments
Possibletocompilebytecodetonativecode
(JIT:Just-In-Time)
Callnative
TypicallyfunctionswritteninC
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Meta-circularevaluator
Meta-circularevaluator
Anevaluatorthatiswritteninthe
samelanguagethatitevaluatesis
saidtobemetacircular(SICP4.1).
Easytoextendthelanguage
Makeiteasiertobuildsophisticated
debuggers
Moresuitedforbuildingnewlanguages
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RPythonandPyPy
PyPyVirtualMachine
Usuallyinterpretersarewritten
inatargetplatformlanguage
suchasC
RPythonisasubsetof
PyPyuses
SourceCode
Compiler
PyPyVM
ByteCode
toprovideasetoftoolsforimplementing
interpretersforanylanguage
apythonimplementationusingthosetools
PyPyVM
PyPyVM
PyPyVM
Windows
Linux
Mac
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BenefitsofRPythonoverhostlanguage
Easiertodevelop
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Conclusion
VirtualMachinesforinterpreting
programs
Stackmachinesareeasier
toimplementbutslower
thanregistermachines
VirtualMachinesintroduce
compilationoverhead,butare
fastertoexecute
IfyouknowPython,youknowRPython
Easiertodebug
SinceyoucanrunRPythonprogramwitha
regularPythoninterpreter
Factortheporttodifferent
platform
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