Bytecode & VM Design

Bytecode & VM Design

devinsampa 2011

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for dummies?

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@qmx

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blog.qmx.me

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whoami?

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geek

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developer @

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instructor @

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opensource freak

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contributor @

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yeah, a freak

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!

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hardcore stuff

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VMs

Unit 1

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Back to basics

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1 + 1?

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10

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logic gates

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law of the instrument

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more flexibility?

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FPGA

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field-_programmable_ gate array

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VHDL

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unix phylosophy

one thing well

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#fail

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generic processing units

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RISC

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RISC

• simple instruction set (1 cycle)
• runs at higher clock
• power efficient !SLIDE

  CISC

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  CISC

• complex instruction set
• microcode support
• powerful !SLIDE

  Register-based CPUs

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  1 + 2 (pseudo asm)

• mov %eax, 1
• mov %ebx, 2
• add %eax, %eax, %ebx !SLIDE

  Register-based CPUs

• Work juggling register slots
• Memory efficient !SLIDE

  WHY?

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  Stack Based CPUs

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  RPN calculators

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  sum(a,b)

• iload_1
• iload_2
• iadd
• ireturn !SLIDE

  The Coffee Machine Problem

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  Free Market

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  Free Market

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  Increasing Abstraction

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  HAL?

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  HAL!

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  Poor man’s Computer

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  interpreter loop

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  tiny VM

  /* simple switch / switch(vm->pProgram->instr[instr_idx]) { case 0x0: break; /* nop / case 0x1: break; / int / case 0x2: *arg0 = *arg1; break; / mov / case 0x3: stack_push(vm->pMemory, arg0); break; / push / case 0x4: stack_pop(vm->pMemory, arg0); break; / pop */ !SLIDE

  JVM

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  JVM

• stack-based VM
• optimizing JIT compiler
• Award-winning Garbage Collection !SLIDE

  Unit 2

  Bytecode

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  the tr00 JVM language

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  limited instruction set

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  256 opcodes, ~206 used

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  static types

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  constant pool

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  constant pool

  const #6 = Asciz main; const #7 = Asciz ([Ljava/lang/String;)V; const #8 = Asciz Hello, world!; const #9 = String #8; / Hello, world! const #10 = Asciz java/lang/System; const #11 = class #10; / java/lang/System const #12 = Asciz out; const #13 = Asciz Lja../../img/PrintStream;; const #14 = NameAndType #12:#13;/ out:Lja../../img/PrintStream; !SLIDE

  stack-based operation

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  stack-based operation

  public static void main(java.lang.String[]); Code: Stack=2, Locals=1, Args_size=1 0: ldc #9; /String Hello, world! 2: getstatic #15; /Field java/lang/System.out:Lja../../img/PrintStream; 5: swap 6: invokevirtual #21; /Method ja../../img/PrintStream.println:(Ljava/lang/Object;)V 9: return } !SLIDE

  invocation strategies

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  static

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  virtual

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  interface

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  interface

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  interface

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  interface

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  New stuff on JDK7

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  dynamic invocation

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  dynamic

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  dynamic

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  dynamic

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  Unit 3

  Optimization

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  the least effort rule

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  if it’s unnecessary, skip it

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  AOT

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  heuristics based

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  heuristics?

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  JIT

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  knowledge based

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  finding the hot spots

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  Inlining

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  inlining

  class Engine def start puts “starting” end end e = Engine.new 1000.times { e.start } !SLIDE

  inlining

  1000.times { puts “starting” } !SLIDE

  de-optimization

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  Garbage Collection

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  sorry, iOS

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  pick yours

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  Serial GC

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  Parallel GC

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  Low Pause

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  G1 GC

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  That’s all folks!

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  ?

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  Thank you!