StackMapAttribute

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org.objectweb.asm.attrs
Class StackMapAttribute

java.lang.Object
  org.objectweb.asm.Attribute
      org.objectweb.asm.attrs.StackMapAttribute

Direct Known Subclasses:: ASMStackMapAttribute

public class StackMapAttribute
extends Attribute
extends Attribute

StackMapAttribute is used by CDLC preverifier. 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;
 }

Author:: Eugene Kuleshov
See Also:: JSR 139 : Connected Limited Device Configuration 1.1

Field Summary
`java.util.List`	`frames` A List of `StackMapFrame` instances.
`(package private) static int`	`MAX_SIZE`

Fields inherited from class org.objectweb.asm.Attribute
`type`

Constructor Summary
`StackMapAttribute()`
`StackMapAttribute(java.util.List frames)`

Method Summary
`StackMapFrame`	`getFrame(Label label)`
`private void`	`getFrameLabels(StackMapFrame frame, java.util.Set labels)`
`java.util.List`	`getFrames()`
`private Label`	`getLabel(int offset, Label[] labels)`
`protected Label[]`	`getLabels()` Returns the labels corresponding to this attribute.
`private void`	`getTypeInfoLabels(java.util.Set labels, java.util.List info)`
`boolean`	`isCodeAttribute()` Returns `true` if this type of attribute is a code attribute.
`boolean`	`isUnknown()` Returns `true` if this type of attribute is unknown.
`protected Attribute`	`read(ClassReader cr, int off, int len, char[] buf, int codeOff, Label[] labels)` Reads a `type` attribute.
`private int`	`readTypeInfo(ClassReader cr, int off, java.util.List info, Label[] labels, char[] buf, boolean isExt, boolean isExtCode)`
`java.lang.String`	`toString()`
`protected ByteVector`	`write(ClassWriter cw, byte[] code, int len, int maxStack, int maxLocals)` Returns the byte array form of this attribute.
`private void`	`writeFrame(StackMapFrame frame, ClassWriter cw, int maxStack, int maxLocals, ByteVector bv)`
`private void`	`writeTypeInfo(ByteVector bv, ClassWriter cw, java.util.List info, int max)`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

Field Detail

MAX_SIZE

static final int MAX_SIZE

See Also:: Constant Field Values

frames

public java.util.List frames

A List of StackMapFrame instances.

Constructor Detail