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Java Virtual Machine: Instruction Set

Java Virtual Machine: Instruction Set. Cheng-Chia Chen. Java Program. class SumI { public static void main (String[] args) { int count=10; int sum =0; for (int index=1;index<count;index++) sum=sum+index; } // method main } // class SumI. 2. Java ByteCode.

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Java Virtual Machine: Instruction Set

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  1. Java Virtual Machine: Instruction Set Cheng-Chia Chen

  2. Java Program class SumI { public static void main (String[] args) { int count=10; int sum =0; for (int index=1;index<count;index++) sum=sum+index; } // method main } // class SumI 2

  3. Java ByteCode Method void main(java.lang.String[]) 0 bipush 10 // byte push 10 to stack (0x10) 2 istore_1 // load 10 (top of stack) to count 3 iconst_0 // push 0 to stack 4 istore_2 // load 0 (top of stack to sum 5 iconst_1 // push 1 to stack 6 istore_3 // load 1 (top of stack) to index 7 goto 17 // go to 17 3

  4. Java ByteCode 10 iload_2 // load sum to stack 11 iload_3 // load index to stack 12 iadd // add 13 istore_2 // store “top of stack” to sum 14 iinc 3 1 // index ++ 17 iload_3 // load index to stack 18 iload_1 // load count to stack 19 if_icmplt 10 // if index < count goto 10 22 return 3

  5. import java.io.*; class ReadFile { public static void main (String[] args) { try { FileInputStream in = new FileInputStream(args[0]); int c; while((c = in.read()) != -1) System.out.println(c); in.close(); } catch(Exception e) { e.printStackTrace(); } } // method main } // class ReadFile

  6. JVM Instruction Sets • Stack and Local Variable Operations • Type Conversion • Integer Arithmetic • Logic and Bit manipulation • Floating Point Arithmetic • Objects and Arrays • Control Flow • Exceptions • Finally Clauses • Method Invocation and Return • Thread Synchronization

  7. Menmonics for instruction type • i for an int operation, • l for long, • s for short, • b for byte, • c for char, • f for float, • d for double, and • a for reference/array. • EX: iload, lload, fload, dload, aload,…

  8. Load and Store Instructions • transfer values between the local variables and the operand stack • load: localVar  Stack • store: Stack  localVar • [i | l | f | d | a]load u8,// or wide load u16 • [i | l | f | d | a]load_<n>, // n=0..3 • [i | l | f | d | a]store u8, // or wide load u16 • [i | l | f | d | a]store_<n>, // n=0..3

  9. Push Constants onto stack • iconst_x • x=m1..5; push int x onto stack. • fconst_x • x=0..2; push float x onto stack. • lconst_x ; dconst_x : • x=0 or 1; push long (or double) x onto stack • aconst_null: push null onto stack. • bipush s8;sipush s16, • push (int) s8 [or (int) s16] onto stack

  10. Push Constants onto stack • ldc u8;ldc_w u16, ldc2_w u16, • push single word (or double worlds for ldc2) from constant_pool entry u8 (or u16) • ldc/ldc_w can be used to push byte/short/char/int/float/String constants.

  11. Generic Stack Operations • nop // do nothing • pop, pop2, // pop top (two) words • dup, dup2, // duplicate top (two) words • swap. // swap top two words • dup_x1, dup_x2 • duplicate top words and put 1 ( 2 ) down • w3, w2, w1 => w3,w1,w2,w1 or (w1,w3,w2,w1) • dup2_x1, dup2_x2, • w4, w3, w2, w1 =>w4, w2,w1, w3,w2,w1 or (w2,w1,w4,w3,w2,w1)

  12. Integer and floating pointArithmetic Instructions • Add: iadd, ladd, fadd, dadd. • Subtract: isub, lsub, fsub, dsub. • Multiply: imul, lmul, fmul, dmul. • Divide: idiv, ldiv, fdiv, ddiv. • Remainder: irem, lrem, frem, drem. • Negate: ineg, lneg, fneg, dneg. • Local variable increment: • iinc u8 s8 // add s8 to lcalvar[u8]. • wide iinc u16 s16 // add s16 to local var at u16

  13. Shift and Bitwise operations • Shift: ishl, ishr, iushr, lshl, lshr, lushr. • ishl : … int2, int1 => … , int2<<(int1 & 0x001f) • lushr: … long2, int1=> … , long2 >>> (int1 & 0x003f) • Bitwise OR: ior, lor. • Bitwise AND: iand, land. • Bitwise exclusive OR: ixor, lxor.

  14. Comparison operations • dcmpg, dcmpl, • …d1,d2=>… int; (d1 < d2 =>-1; d2=d1=> 0; d1>d2 =>1 ) or NaN=>(g =>1; l=>-1) • fcmpg, fcmpl, // like above • lcmp. • … long1, long2 => … int k where • k = -1, 0 or 1 depending on long1 <, = or > long2.

  15. Type Conversion Instructions • widening conversions: • int  long  float  double : • i2l, i2f, i2d, l2f, l2d, f2d. • // sign extension+round-to-nearest mode • Narrowing conversions: • double  float  long  int : • d2f, d2l, d2i, f2l, f2i, l2i // truncate+ sign extension+ rtn mode • int  short, byte, char: • i2s, i2c, i2b // truncate+ sign extension • Note: byte, short, char  int are done automaticaly.

  16. Object Creation and Field Access • new • Create a new class instance on the heap, • and push a reference: • Field access: • getfield fieldRefIndex;putfield fieldRefIndex, • … objRef  … value; …objRef, value … • getstaticfieldRefIndexputstatic fieldRefIndex • …  value; …value  … • Type Checking: • instanceof class_index : … objRef  … RltVal • checkcast class_index: …obj1  … obj1 if obj1 can be casted to class type, o/w throw CastException

  17. Array Creation • newarray aType: • pop length, allocate new primitive array of type given by atype, push the reference. • aType : (z,c,f,d,b,s,i,l) ->(4,5,6,7,8,9,10,11) • … u16 -> arrayRef • anewarray Class_index, • pop length, allocate new array of type given by class_index, push the reference • multianewarray type_index dim:u8. • pop dim number of array lengths, allocate multi-dimensional array of type class_index, pop reference. • new int[10][20] ==> p10, p20, multianewarray [[i 2.

  18. Array Component Access • array component  stack : • baload, caload, saload, iaload, • … arrayRef, index:s32  … (int) array[index] • laload, faload, daload, aaload. • stack  array component • bastore, castore, sastore, iastore, • … arrayRef, index:s32, val  … • lastore, fastore, dastore, aastore. • Get the length of array:arraylength • … arrayRef  … (int)array.length

  19. Control flow Instructions1. Conditional Branches • Conditional branch: • unary comparsions • ifeq, iflt, ifle, ifne, ifgt, ifge, // =0?, <0?,… • ifnull, ifnonnull, // null or not null • binary comparisons • if_icmpeq, if_icmpne, if_icmplt, if_icmpgt, if_icmple, if_icmpge, • if_acmpeq, if_acmpne. // compare reference • For comparison of long, double and float • use dcmpg, dcmpl, fcmpg, fcmpl, lcmp and • unary comparisons on int.

  20. Control flow Instructions :2.Compound Conditional Branches • lookupswitch <0-3bytepads for word alignment> defaultOffset#pairs {caseoffset}#pairs: • all (blue) fields are int32 values • case must be in ascending order • e.g.: lookupswitch lab0 3 2 lab1 10 lab2 13 lab3 • tableswitch <0-3pads> defOffset lowCase highCase offset high-low+1. • goto offset[top-low+1] iff low ≤ top ≤ high • else goto defOffset. • e.g.: tableswitch lab0 11 14 lab11 lab12 lab13 lab14.

  21. Control flow Instructions: Unconditional branches • goto s16;goto_w s32 • pc = pc + s16 (or s32). // for implementing finally clauses // intraMethod subroutine call • jsr s16,jsr_w s32, • push return addr and jumpToSubroutine pc+s16 for a finally block • …  … returnAddr • ret u8; widen ret u16, • return to addr given by localVar u8 or u16 .

  22. Method Invocation and Return Instructions • invokevirtual : for normal methods • invokeInterface: • for interface methods // search of implementation is needed • invokespecial: • for private method, superclass method and instance initialization (constructors) methods • invokestatic : for static methods • format: opcode u16// methodRefIndex • return : • ireturn, lreturn, freturn, dreturn, areturn • return : for void, instance, class (or interface) initialization methods

  23. Exceptions related Instructions • Throw Exception: • athrow • can also be thrown by other instructions if abnormal condition detected. • … ExcObj  … • Implementing finally • jsr s16,jsr_w s32, • jumpToSubroutine pc+s16 for a finally block • ret u8; widen ret u16, • return to addr given by localVar u8 or u16 .

  24. Synchronization • via monitor construct: • monitorenter, monitorexit • monitorenter • pop objectref, acquire the lock associated with the object. • … ObjRef  … • monitorexit • pop objectref, release the lock associate with objectref • … ObjRef  …

  25. Classes needing special support of JVM • Reflection: • java.lang.reflect.* and java.lang.Class. • Loading and creation of a class or interface. • ClassLoader. • Linking and initialization of a class or interface. • Security: • java.security.** and other classes such as SecurityManager. • Multithreading, such as the class Thread. • Weak references: java.lang.ref.* • …

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