org.objectweb.asm.attrs

Class StackMapAttribute

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,

   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;
   }
 

Author: Eugene Kuleshov

See Also: JSR 139 : Connected Limited Device Configuration 1.1

Field Summary
ArrayListframes
Constructor Summary
StackMapAttribute()
Method Summary
StackMapFramegetFrame(Label label)
protected Label[]getLabels()
protected Attributeread(ClassReader cr, int off, int len, char[] buf, int codeOff, Label[] labels)
StringtoString()
protected ByteVectorwrite(ClassWriter cw, byte[] code, int len, int maxStack, int maxLocals)

Field Detail

frames

public ArrayList frames

Constructor Detail

StackMapAttribute

public StackMapAttribute()

Method Detail

getFrame

public StackMapFrame getFrame(Label label)

getLabels

protected Label[] getLabels()

read

protected Attribute read(ClassReader cr, int off, int len, char[] buf, int codeOff, Label[] labels)

toString

public String toString()

write

protected ByteVector write(ClassWriter cw, byte[] code, int len, int maxStack, int maxLocals)