org.objectweb.asm.attrs
Class StackMapAttribute

java.lang.Object
  extended by org.objectweb.asm.Attribute
      extended by org.objectweb.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,

   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
 ArrayList frames
           
 
Fields inherited from class org.objectweb.asm.Attribute
next, type
 
Constructor Summary
StackMapAttribute()
           
 
Method Summary
 StackMapFrame getFrame(Label label)
           
protected  Label[] getLabels()
          Returns the labels corresponding to this attribute.
protected  Attribute read(ClassReader cr, int off, int len, char[] buf, int codeOff, Label[] labels)
          Reads a type attribute.
 String toString()
           
protected  ByteVector write(ClassWriter cw, byte[] code, int len, int maxStack, int maxLocals)
          Returns the byte array form of this attribute.
 
Methods inherited from class org.objectweb.asm.Attribute
isUnknown
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Field Detail

frames

public ArrayList frames
Constructor Detail

StackMapAttribute

public StackMapAttribute()
Method Detail

getFrame

public StackMapFrame getFrame(Label label)

read

protected Attribute read(ClassReader cr,
                         int off,
                         int len,
                         char[] buf,
                         int codeOff,
                         Label[] labels)
Description copied from class: Attribute
Reads a type attribute. This method must return a new Attribute object, of type type, corresponding to the len bytes starting at the given offset, in the given class reader.

Overrides:
read in class Attribute
Parameters:
cr - the class that contains the attribute to be read.
off - index of the first byte of the attribute's content in cr.b. The 6 attribute header bytes, containing the type and the length of the attribute, are not taken into account here.
len - the length of the attribute's content.
buf - buffer to be used to call readUTF8, readClass or readConst.
codeOff - index of the first byte of code's attribute content in cr.b, or -1 if the attribute to be read is not a code attribute. The 6 attribute header bytes, containing the type and the length of the attribute, are not taken into account here.
labels - the labels of the method's code, or null if the attribute to be read is not a code attribute.
Returns:
a new Attribute object corresponding to the given bytes.

write

protected ByteVector write(ClassWriter cw,
                           byte[] code,
                           int len,
                           int maxStack,
                           int maxLocals)
Description copied from class: Attribute
Returns the byte array form of this attribute.

Overrides:
write in class Attribute
Parameters:
cw - the class to which this attribute must be added. This parameter can be used to add to the constant pool of this class the items that corresponds to this attribute.
code - the bytecode of the method corresponding to this code attribute, or null if this attribute is not a code attributes.
len - the length of the bytecode of the method corresponding to this code attribute, or null if this attribute is not a code attribute.
maxStack - the maximum stack size of the method corresponding to this code attribute, or -1 if this attribute is not a code attribute.
maxLocals - the maximum number of local variables of the method corresponding to this code attribute, or -1 if this attribute is not a code attribute.
Returns:
the byte array form of this attribute.

getLabels

protected Label[] getLabels()
Description copied from class: Attribute
Returns the labels corresponding to this attribute.

Overrides:
getLabels in class Attribute
Returns:
the labels corresponding to this attribute, or null if this attribute is not a code attribute that contains labels.

toString

public String toString()
Overrides:
toString in class Object