org.objectweb.asm.attrs
Class StackMapAttribute
public class StackMapAttribute
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;
}
List | frames - A List of
StackMapFrame instances.
|
frames
public List frames
A List of StackMapFrame
instances.
StackMapAttribute
public StackMapAttribute()
StackMapAttribute
public StackMapAttribute(List frames)
getFrames
public List getFrames()
getLabels
protected Label[] getLabels()
Returns the labels corresponding to this attribute.
- getLabels in interface Attribute
- the labels corresponding to this attribute, or null if
this attribute is not a code attribute that contains labels.
isCodeAttribute
public boolean isCodeAttribute()
Returns true if this type of attribute is a code attribute.
- isCodeAttribute in interface Attribute
- true if this type of attribute is a code attribute.
isUnknown
public boolean isUnknown()
Returns true if this type of attribute is unknown. The default
implementation of this method always returns true.
- isUnknown in interface Attribute
- true if this type of attribute is unknown.
read
protected Attribute read(ClassReader cr,
int off,
int len,
char[] buf,
int codeOff,
Label[] labels)
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.
- read in interface Attribute
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.
- a new
Attribute
object corresponding to the given
bytes.
toString
public String toString()
write
protected ByteVector write(ClassWriter cw,
byte[] code,
int len,
int maxStack,
int maxLocals)
Returns the byte array form of this attribute.
- write in interface Attribute
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.
- the byte array form of this attribute.