jef.dna.instructions.impl
Class LookupSwitch

java.lang.Object
  jef.dna.instructions.impl.InstructionAncestor
      jef.dna.instructions.impl.LookupSwitch

All Implemented Interfaces:

java.lang.Cloneable, Instruction, BytesCountable

public class LookupSwitch
extends InstructionAncestor

This class maps the LOOKUPSWITCH bytecode instruction.
A lookupswitch is a variable-length instruction. Immediately after the lookupswitch opcode, between zero and three null bytes (zeroed bytes, not the null object) are inserted as padding. The number of null bytes is chosen so that the defaultbyte1 begins at an address that is a multiple of four bytes from the start of the current method (the opcode of its first instruction).

Immediately after the padding follow a series of signed 32-bit values: default, npairs, and then npairs pairs of signed 32-bit values. The npairs must be greater than or equal to 0. Each of the npairs pairs consists of an int match and a signed 32-bit offset. Each of these signed 32-bit values is constructed from four unsigned bytes as (byte1 << 24) | (byte2 << 16) | (byte3 << 8) | byte4. The table match-offset pairs of the lookupswitch instruction must be sorted in increasing numerical order by match.

The key must be of type int and is popped from the operand stack. The key is compared against the match values. If it is equal to one of them, then a target address is calculated by adding the corresponding offset to the address of the opcode of this lookupswitch instruction.
If the key does not match any of the match values, the target address is calculated by adding default to the address of the opcode of this lookupswitch instruction. Execution then continues at the target address. The target address that can be calculated from the offset of each match-offset pair, as well as the one calculated from default, must be the address of an opcode of an instruction within the method that contains this lookupswitch instruction.

Author:

ggiovanzana

Field Summary

Fields inherited from class jef.dna.instructions.impl.InstructionAncestor

logger, opCode, operands, operandsCount

Constructor Summary

LookupSwitch()
Creates a new instance of LookupSwitch

Method Summary

void	setOperandsCountPosticipated(int[] bytecode, int startFrom) This method should be implemented by those classes wrapping JVM instructions whose number of operands is variable.
int	updateRefs(int offset) This method must implement the logic necessary to update all the references to constant pool table's entries contained within the bytecode instruction.

Methods inherited from class jef.dna.instructions.impl.InstructionAncestor

clone, fromArray, getBytesCount, getOpCode, getOperands, getOperandsCount, setOpCode, setOperands, toArray

Methods inherited from class java.lang.Object

equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

LookupSwitch

public LookupSwitch()

Creates a new instance of LookupSwitch

Method Detail

setOperandsCountPosticipated

public void setOperandsCountPosticipated(int[] bytecode,
                                         int startFrom)

This method should be implemented by those classes wrapping JVM instructions whose number of operands is variable. This method is called by the fromArray method defined in the InstructionAncestor class. InstructionAncestor already contains an empty implementation of this method, useful for those classes exposing a prefixed number of operands. In such a case there is no need to override the setOperandsCountPosticipated method,

Specified by:

setOperandsCountPosticipated in interface Instruction

Overrides:

setOperandsCountPosticipated in class InstructionAncestor

Parameters:

bytecode - The method's bytecode

startFrom - The index of the current instruction's mnemonic (opcode)

updateRefs

public int updateRefs(int offset)

This method must implement the logic necessary to update all the references to constant pool table's entries contained within the bytecode instruction.

Specified by:

updateRefs in interface Instruction

Overrides:

updateRefs in class InstructionAncestor

Parameters:

offset - The offset used for updating expressed as number of cpt's entries to be skipped

Returns:

int The number of processed words within the current bytecode instruction