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oracle.toplink.libraries.asm.attrs
Class StackMapAttribute

java.lang.Object
oracle.toplink.libraries.asm.Attribute
oracle.toplink.libraries.asm.attrs.StackMapAttribute

Direct Known Subclasses:

ASMStackMapAttribute

public class StackMapAttribute

extends Attribute

StackMapAttribute is used by CDLC preverifier and also by javac compiller starting from J2SE 1.5. Definition is given in appendix "CLDC Byte Code Typechecker Specification" from CDLC 1.1 specification.

Note that this implementation does not calculate StackMapFrame structures from the method bytecode. If method code is changed or generated from scratch, then developer is responsible to prepare a correct StackMapFrame structures.

The format of the stack map in the class file is given below. In the following,

• if the length of the method's byte code1 is 65535 or less, then uoffset represents the type u2; otherwise uoffset represents the type u4.
• If the maximum number of local variables for the method is 65535 or less, then ulocalvar represents the type u2; otherwise ulocalvar represents the type u4.
• If the maximum size of the operand stack is 65535 or less, then ustack represents the type u2; otherwise ustack represents the type u4.

   stack_map { // attribute StackMap
     u2 attribute_name_index;
     u4 attribute_length
     uoffset number_of_entries;
     stack_map_frame entries[number_of_entries];
   }
 

Each stack map frame has the following format:

   stack_map_frame {
     uoffset offset;
     ulocalvar number_of_locals;
     verification_type_info locals[number_of_locals];
     ustack number_of_stack_items;
     verification_type_info stack[number_of_stack_items];
   }
 

The verification_type_info structure consists of a one-byte tag followed by zero or more bytes, giving more information about the tag. Each verification_type_info structure specifies the verification type of one or two locations.

   union verification_type_info {
     Top_variable_info;
     Integer_variable_info;
     Float_variable_info;
     Long_variable_info;
     Double_variable_info;
     Null_variable_info;
     UninitializedThis_variable_info;
     Object_variable_info;
     Uninitialized_variable_info;
   }

   Top_variable_info {
     u1 tag = ITEM_Top; // 0
   }

   Integer_variable_info {
     u1 tag = ITEM_Integer; // 1
   }

   Float_variable_info {
     u1 tag = ITEM_Float; // 2
   }

   Long_variable_info {
     u1 tag = ITEM_Long; // 4
   }

   Double_variable_info {
     u1 tag = ITEM_Double; // 3
   }

   Null_variable_info {
     u1 tag = ITEM_Null; // 5
   }

   UninitializedThis_variable_info {
     u1 tag = ITEM_UninitializedThis; // 6
   }

   Object_variable_info {
     u1 tag = ITEM_Object; // 7
     u2 cpool_index;
   }

   Uninitialized_variable_info {
     u1 tag = ITEM_Uninitialized // 8
     uoffset offset;
   }
 

See Also:

JSR 139 : Connected Limited Device Configuration 1.1

Field Summary

java.util.ArrayList

frames

Fields inherited from class oracle.toplink.libraries.asm.Attribute

next, type

Constructor Summary

StackMapAttribute()

Method Summary

StackMapFrame	getFrame(Label label)
java.lang.String	toString()

Methods inherited from class oracle.toplink.libraries.asm.Attribute

isUnknown

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

frames

public java.util.ArrayList frames

Constructor Detail

StackMapAttribute

public StackMapAttribute()

Method Detail

getFrame

public StackMapFrame getFrame(Label label)

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object

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