JASM Syntax

This chapter describes JASM syntax, and how to encode class files using this syntax. Jasm is a java assembler that accepts text in the JASM format and produces a .class file for use with a Java Virtual Machine. Jasm's primary use is as a tool for producing specialized tests for testing a JVM implementation

This chapter describes JASM syntax in the following sections:

General Syntax

JASM syntax can come in one of two variations: short-form or verbose-form.  Short form uses Java-style names to refer to items in a constant-pool.  Verbose form uses explicit constant-pool indexes to refer to items in the constant pool.  The normal output from JDIS produces jasm files in the short-form.  Using the -g option for JDIS (ie.  jdis -g file.class) produces JASM source in the verbose-form.

The source text file can be free form (newlines are considered blanks) and may contain Java-style commenting. The first line of a JASM file represents the name of the resulting file in the destination directory. This name does not affect the content of the resulting file. This line has two forms:

file FILENAME 

or

class CLASSNAME 

In the latter case, extension .class will be added to form FILENAME. Jasm's -d option allows you to define the destination directory. A list of structured data items follows the class name. The length (in bytes) of each item is determined by its representation.

Description formats

Lexical Structure

The source text file can be free form (newlines, tabs, and blank spaces are equivalent). Additionally, the source may contain standard Java and C++ comments.

STRING, NUMBER, and IDENT are treated the same as in the Java Language Specification. One difference is that LETTERs include also `/', `<', `>', `(', and `)' .

      abstract final interface native private protected public static super synchronized

      transient volatile deprecated synthetic bridge varargs

Not all access bits make sense for all declarations: for example, the "super" and "interface" access flags are applied to classes only.

If an access bit is used improperly, the assembler prints a warning, but places the bit in the access set.

Note that deprecated and synthetic keywords are not translated to access flags in the Java sense. For these jasm generates a corresponding Deprecated or Synthetic attributes instead of access bits. The synthetic access flag is used to mark compiler generated members not seen in the source (for example, a field reference to an anonymous outer class).

TAG: one of

      int float long double Asciz String class Field Method NameAndType 
 InterfaceMethod MethodType MethodHandle InvokeDynamic

 

Local names represent labels, trap-labels and local variables. Their scope is constrained by method parenthesis.

 

LOCAL_NAME:

      IDENT

CONSTANT_INDEX:

      #NUMBER

 

Each CONSTANT_INDEX represents a reference into the constant pool at the specified location.

General Class Structure

INTERFACES: list of

      CONSTANT_CELL(class)

TOP_LEVEL_COMPONENT: one of

      CONSTANT_DECLARATION FIELD_DECLARATION METHOD_DECLARATION INNER_CLASS_DECARATIONS

CLASS: sequence of

    ANNOTATIONS CLASS_ACCESS CONSTANT_CELL(class) [extends CONSTANT_CELL(class)] 
    [implements INTERFACES] [version INTEGER:INTEGER] { [TOP_LEVEL_COMPONENT...] }

CLASS_ACCESS: list of

    [public][final][super][interface][abstract][synthetic][annotation][enum]

 

The extends CONSTANT_CELL(class) clause places the "super" element of the class file. The implements INTERFACES clause places the table of interfaces. Since the assembler does not distinguish interfaces and ordinary classes (the only difference is one access bit), the table of interfaces of an interface class must be declared with implements keyword, and not extends, as in Java language.

Note:The last two rules allow TOP_LEVEL_COMPONENT to appear in any order and number. For example, you can split constant pool table into several parts, mixing constants and method declarations.

General Source File Structure

 

PACKAGE_DECLARATION:

    package IDENT;

 

Package declaration can appear only once in source file.

 

SOURCE_FILE: sequence of

    PACKAGE_DECLARATION CLASS...

 

The Constant Pool and Constant Elements

A CONSTANT_CELL refers to an element in the constant pool. It may refer to the element either by its index or its value:

 

CONSTANT_CELL:

    CONSTANT_INDEX

    TAGGED_CONSTANT_VALUE

 

Generic rule for TAGGED_CONSTANT_VALUE is:

 

TAGGED_CONSTANT_VALUE:

    [TAG] CONSTANT_VALUE

 

A TAG may be omitted when the context only allows one kind of a tag. For example, the argument of an anewarray instruction should be a CONSTANT_CELL which represents a class, so instead of

    anewarray class java/lang/Object

one may write:

    anewarray java/lang/Object

It is possible to write another tag, e.g.:

    anewarray String java/lang/Object

However, the resulting program will be incorrect.

Another example of an implicit tag (eg. a context which implies tag) is the header of a class declaration. You may write:

    aClass {
    }

which is equivalent to:

    class aClass {
    }

Below, the tag implied by context will be included in the rules, e.g.:

    CONSTANT_VALUE(int).

The exact notation of CONSTANT_VALUE depends on the (explicit or implicit) TAG.

 

TAGGED_CONSTANT_VALUE:

INTEGER
[INTEGER|LONG]
[FLOAT|INTEGER]
bits INTEGER
[FLOAT|DOUBLE|INTEGER|LONG]
[bits INTEGER | bits LONG]
EXTERNAL_NAME
CONSTANT_NAME
CONSTANT_NAME
NAME_AND_TYPE
CONSTANT_FIELD
CONSTANT_FIELD
INVOKESUBTAG	:	CONSTANT_FIELD [FIELDREF|METHODREF|INTERFACEMETHODREF]
CONSTANT_NAME
INVOKESUBTAG	:	CONSTANT_FIELD	:	NAME_AND_TYPE	[INVOKEDYNAMIC_STATIC_ARGS]

 

 

Note

When the JASM parser encounters an InvokeDynamic constant, it creates an entry in the BootstrapMethods attribute (the BootstrapMethods attribute is produced if it has not already been created). The entry contains a reference to the MethodHandle item in the constant pool, and, optionally, a sequence of references to additional static arguments (ldc-type constants) to the bootstrap method.

INVOKESUBTAGs for MethodHandle and (const) InvokeDynamic are defined as follows:

 

INVOKESUBTAG:

REF_GETFIELD	[1]
REF_GETSTATIC	[2]
REF_PUTFIELD	[3]
REF_PUTSTATIC	[4]
REF_INVOKEVIRTUAL	[5]
REF_INVOKESTATIC	[6]
REF_INVOKESPECIAL	[7]
REF_NEWINVOKESPECIAL	[8]
REF_INVOKEINTERFACE	[9]

 

Static arguments for an InvokeDynamic constant are defined as follows:

 

INVOKEDYNAMIC_STATIC_ARGUMENTS:

    INVOKEDYNAMIC_STATIC_ARG ',' ...

INVOKEDYNAMIC_STATIC_ARG: (one of)

    INVOKEDYNAMIC_STATIC_ARG_CONSTANT_VALUE

INVOKEDYNAMIC_STATIC_ARG_CONSTANT_VALUE:

int	INTEGER
long	[INTEGER|LONG]
float	[FLOAT|INTEGER]
double	[FLOAT|DOUBLE|INTEGER|LONG]
class	CONSTANT_NAME
String	CONSTANT_NAME
MethodHandle	INVOKESUBTAG:CONSTANT_FIELD
MethodType	CONSTANT_NAME

 

INTEGER, LONG, FLOAT, and DOUBLE correspond to IntegerLiteral and FloatingPointLiteral as described in The Java Language Specification. If a double-word constant (LONG or DOUBLE) is represented with a single-word value (INTEGER or FLOAT, respectively), single-word value is simply promoted to double-word, as described in The Java Language Specification. If floating-point constant (FLOAT or DOUBLE) is represented with an integral value (INTEGER or LONG, respectively), the result depends on whether the integral number is preceded with the keyword "bits". If "bits" is not used, the result is a floating-point number closest in value to the decimal number. If the keyword "bits" is used, the floating-point constant takes bits of the integral value without conversion.

Thus,

   float 2;

means the same as

   float 2.0f;

and the same as

   float bits 0x40000000;

while

   float bits 2;

actually means the same as

   float bits 0x00000002;

and the same as

   float 2.8026e-45f

 

CONSTANT_NAME:

    CONSTANT_INDEX

    EXTERNAL_NAME

EXTERNAL_NAME:

    IDENT STRING

 

External names are names of class, method, field, or type, which stay in resulting .class file, and may be represented both by IDENT or by STRING (which is useful when name contains non-letter characters).

 

NAME_AND_TYPE:

    CONSTANT_INDEX

    CONSTANT_NAME:CONSTANT_NAME

 

In this second example, the first CONSTANT_NAME denotes the name of a field and second denotes its type.

 

CONSTANT_FIELD:

    CONSTANT_INDEX

    [CONSTANT_NAME.]NAME_AND_TYPE

 

In this third example, CONSTANT_NAME denotes to the class of a field. If CONSTANT_NAME is omitted, the current class is assumed.

Constant Declarations

Constant declarations are demonstrated in the examples below:

	const #1=int 1234
	    , #2=String "a string"
	    , #3=Method get:I
	;

 

CONSTANT_DECLARATION:

    const CONSTANT_DECLARATORS ;

CONSTANT_DECLARATORS: list of

    CONSTANT_DECLARATOR

CONSTANT_DECLARATOR:

    CONSTANT_INDEX = TAGGED_CONSTANT_VALUE

 

Field Variables

 

FIELD_DECLARATION:

    ANNOTATIONS FIELD_ACCESS Field FIELD_DECLARATORS ;

FIELD_DECLARATORS: list of

    FIELD_DECLARATOR

FIELD_DECLARATOR:

    EXTERNAL_NAME:CONSTANT_NAME [ = TAGGED_CONSTANT_VALUE ]

FIELD_ACCESS: list of

    [public|private|protected][final][static][volatile][transient][synthetic][enum]

 

Example:

	public static Field 
	    field1:I = int 1234,
	    field2:S 
	;

Access bits (public and static) are applied both to field1 and field2. The EXTERNAL_NAME denotes the name of the field, CONSTANT_NAME denotes its type, TAGGED_CONSTANT_VALUEdenotes initial value.

Method Declarations

 

METHOD_DECLARATION: sequence of

    ANNOTATIONS METHOD_ACCESS Method

    EXTERNAL_NAME:CONSTANT_NAME

    [THROWS]

    STACK_SIZE

    [LOCAL_VAR_SIZE]

    { INSTRUCTION_STATEMENT... }

 

The EXTERNAL_NAME denotes the name of the method, CONSTANT_NAME denotes its type.

 

METHOD_ACCESS: list of

    [public|private|protected][static][final][synthetic][bridge][varargs]
    [native][abstract][strict][synthetic]

THROWS:

    throws EXCEPTIONS

EXCEPTIONS: list of

    CONSTANT_CELL(class)

 

The meaning of the THROWS clause is the same as in Java Language Specification - it forms Exceptions attribute of a method. Jasm itself does not use this attribute in any way.

 

STACK_SIZE:

    stack NUMBER

 

The NUMBER denotes maximum operand stack size of the method.

 

LOCAL_VAR_SIZE:

    locals NUMBER

 

The NUMBER denotes number of local variables of the method. If omitted, it is calculated by assembler according to the signature of the method and local variable declarations.

Instructions

 

VM Instructions

INSTRUCTION_STATEMENT:

    [NUMBER] [LABEL:] INSTRUCTION|PSEUDO_INSTRUCTION ; 

 

Jasm allows for a NUMBER (which is ignored) at the beginning of each line. This is allowed in order to remain consistent with the jdis disassembler. Jdis puts line numbers in disassembled code that may be reassembled using Jasm without any additional modifications.

INSTRUCTION:

    OPCODE [ARGUMENTS]

ARGUMENTS: list of

    ARGUMENT

ARGUMENT:

    NUMBER LABEL LOCAL_VARIABLE TRAP_IDENT CONSTANT_CELL SWITCHTABLE TYPE

LABEL:

    NUMBER IDENT

LOCAL_VARIABLE:

    NUMBER IDENT

TRAP_IDENT:

    IDENT

TYPE:

    NUMBER boolean byte char int float long double class

SWITCHTABLE:

    { [NUMBER:LABEL...] [default:LABEL] }

 

 

SWITCHTABLE example: Java_text

     switch (x) {
     	case 11:
	 		x=1;
	 		break;
     	case 12:
	 		x=2;
	 		break;
     	default:
	 		x=3;
     }

will be coded in assembler as follows:

tableswitch  {
	 11: L24;
	 12: L29;
	 default: L34
     }
L24: iconst_1; 
     istore_1;
     goto  L36;
L29: iconst_2 ;
     istore_1;
     goto  L36;
L34: iconst_3; 
     istore_1;
L36:    ....

OPCODE is any mnemocode from the instruction set. If mnemocode needs an ARGUMENT, it cannot be omitted. Moreover, the kind (and number) of the argument(s) must match the kind (and number) required by the mnemocode:

aload, astore, fload, fstore, iload, istore, lload, lstore, dload, dstore, ver, endvar:	LOCAL_VARIABLE
iinc:	LOCAL_VARIABLE, NUMBER
sipush, bipush, bytecode:	NUMBER
tableswitch, lookupswitch:	SWITCHTABLE
newarray:	TYPE
jsr, goto, ifeq, ifge, ifgt, ifle, iflt, ifne, if_icmpeq, if_icmpne, if_icmpge, if_icmpgt, if_icmple, if_icmplt, if_acmpeq, if_acmpne, ifnull, ifnonnull, try, endtry:	LABEL
jsr_w, goto_w:	LABEL
ldc_w, ldc2_w, ldc:	CONSTANT_CELL
new, anewarray, instanceof, checkcast,	CONSTANT_CELL(class)
multianewarray	NUMBER, CONSTANT_CELL(class)
putstatic, getstatic, putfield, getfield:	CONSTANT_CELL(Field)
invokevirtual, invokenonvirtual, invokestatic:	CONSTANT_CELL(Method)
invokeinterface:	NUMBER, CONSTANT_CELL(Method)
invokedynamic:	CONSTANT_CELL(InvokeDynamic)
aaload,  aastore,  aconst_null,  aload_0,  aload_1,  aload_2,  aload_3,  aload_w ,  areturn,  arraylength,  astore_0,  astore_1,  astore_2,  astore_3,  astore_w,  athrow,  baload,  bastore,  caload,  castore,  d2f,  d2i,  d2l,  dadd,  daload,  dastore,  dcmpg,  dcmpl,  dconst_0,  dconst_1,  ddiv,  dead,  dload_0,  dload_1,  dload_2,  dload_3,  dload_w ,  dmul,  dneg,  drem,  dreturn,  dstore_0,  dstore_1,  dstore_2,  dstore_3,  dstore_w,  dsub,  dup,  dup2,  dup2_x1,  dup2_x2,  dup_x1,  dup_x2,  f2d,  f2i,  f2l,  fadd,  faload,  fastore,  fcmpg,  fcmpl,  fconst_0,  fconst_1,  fconst_2,  fdiv,  fload_0,  fload_1,  fload_2,  fload_3,  fload_w,  fmul,  fneg,  frem,  freturn ,  fstore_0,  fstore_1,  fstore_2,  fstore_3,  fstore_w,  fsub ,  i2b,  i2c,  i2d,  i2f,  i2l,  i2s,  iadd,  iaload,  iand,  iastore,  iconst_0,  iconst_1,  iconst_2,  iconst_3,  iconst_4,  iconst_5,  iconst_m1,  idiv,  iinc_w,  iload_0,  iload_1,  iload_2,  iload_3,  iload_w,  imul,  ineg,  int2byte,  int2char,  int2short,  ior,  irem,  ireturn,  ishl,  ishr,  istore_0,  istore_1,  istore_2,  istore_3,  istore_w,  isub,  iushr,  ixor,  l2d,  l2f,  l2i,  label,  ladd,  laload,  land,  lastore,  lcmp,  lconst_0,  lconst_1,  ldiv,  lload_0,  lload_1,  lload_2,  lload_3,  lload_w,  lmul,  lneg,  lor,  lrem,  lreturn,  lshl,  lshr,  lstore_0,  lstore_1,  lstore_2,  lstore_3,  lstore_w,  lsub,  lushr,  lxor,  monitorenter,  monitorexit,  nonpriv,  nop,  pop,  pop2,  priv,  ret,  return,  ret_w,  saload,  sastore,  swap,   wide	<No Arguments>

 

InvokeDynamic Instructions

InvokeDynamic instructions are instructions that allow dynamic binding of methods to a call site. These instructions in JASM form are rather complex, and the JASM assembler does some of the necessary work to create a BootstrapMethods attribute for entries of binding methods.

class Test
        version 51:0
{


   Method m:"()V"
     stack 0 locals 1
   {
       invokedynamic REF_invokeSpecial:bsmName:"()V"
          // information about bootstrap method
                                      :methName:"(I)I" 
          // dynamic call-site name ("methName") 
          // plus the argument and return types of the call ("(I)I")
                                      int 1, long 2l;  
          // optional sequence of additional static arguments to the 
          // bootstrap method (ldc-type constants)
   }

} // end Class Test

 

his JASM code has an invokedynamic instruction of the form:

 

invokedynamic (CONSTANT_CELL(INVOKEDYNAMIC))

 

where the INVOKEDYNAMIC constant is represented as specified

 

invokedynamic INVOKESUBTAG : CONSTANT_FIELD (bootstrapmethod signature) : NAME_AND_TYPE (CallSite) [Arguments (Optional)]

The JASM assembler creates the appropriate constant entries and entries into the BootstrapMethods attribute in a resulting class file.

You can also create InvokeDynamic constants and BootstrapMethods explicitly:

	#22; //class Test3
	version 51:0
{

const #1 = InvokeDynamic	0:#11;	
     //  REF_invokeSpecial:Test3.bsmName:"()V":name:"(I)I" int 1, long 2l
const #2 = Asciz	"Test3";
const #3 = long	2l;
const #5 = class	#6;	//  java/lang/Object
const #6 = Asciz	"java/lang/Object";
const #7 = Asciz	"name";
const #8 = int	1;
const #9 = Asciz	"SourceFile";
const #10 = Asciz	"Test3.jasm";
const #11 = NameAndType	#7:#21;	//  name:"(I)I"
const #12 = Asciz	"()V";
const #13 = Method	#22.#17;	//  Test3.bsmName:"()V"
const #14 = Asciz	"Code";
const #15 = Asciz	"m";
const #16 = Asciz	"BootstrapMethods";
const #17 = NameAndType	#20:#12;	//  bsmName:"()V"
const #18 = Asciz	"LineNumberTable";
const #19 = MethodHandle	7:#13;	//  REF_invokeSpecial:Test3.bsmName:"()V"
const #20 = Asciz	"bsmName";
const #21 = Asciz	"(I)I";
const #22 = class	#2;	//  Test3
const #23 = class	#6;	//  java/lang/Object



Method #15:#12
	stack 0 locals 1
{
	0:	invokedynamic	#1; 
   //	InvokeDynamic REF_invokeSpecial:Test3.bsmName:"()V":name:"(I)I" int 1, long 2l;
}

BootstrapMethod #19 #8 #3;

} // end Class Test3

 

In this example, const #1 = InvokeDynamic 0:#11; is the InvokeDynamic constant that refers to BootstrapMethod at index '0' in the BootstrapMethods Attribute (BootstrapMethod #19 #8 #3; which refers to the MethodHandle at const #19, plus 2 other static args (at const #8 and const #3).

 

Pseudo Instructions

Pseudo instructions are 'assembler directives', and not really instructions (in the VM sense) They typically come in two forms: Code-generating Pseudo-Instructions, and Attribute-Generating Pseudo-Instructions.

Code-Generating Pseudo-Instructions

The bytecode directive instructs the assembler to put a collection of raw bytes into the code attribute of a method:

bytecode NUMBERS

    NUMBERS is list of NUMBERs (divided by COMMA).

 Inserts bytes in place of the instruction. May have any number of numeric arguments, each of them to be converted into a byte and inserted in method's code.

Attribute-Generating Pseudo-Instructions

The rest of pseudo_instructions do not produce any bytecodes, and are used to form tables: local variable table, exception table,
Stack Maps, and Stack Map Frames. Line Number Tables can not be specified, but they are constructed by the assembler itself.

 

Local Variable Table Attribute Generation

 

var LOCAL_VARIABLE

    Starts local variable range

endvar LOCAL_VARIABLE

    Ends local variable range. LOCAL_VARIABLE means name or index of local variable table entry.

 

 

Example:

static void main (String[] args) {
	Tester inst = new Tester();
    inst.callSub();
}

 

will be coded in assembler as follows:

static Method #8:#9	 // main:"([Ljava/lang/String;)V"
	stack 2 locals 2
{
4 var 0; // args:"[Ljava/lang/String;".
	0:	new	#1; //	class Tester;
	3:	dup;
	4:	invokespecial	#2; //	Method "<init>":"()V";
	7:	astore_1;
6 var 1; // inst:"LTester
	8:	aload_1;
	9:	invokevirtual	#3; //	Method callSub:"()V";
7	12:	return;
 endvar 0, 1;	
}

 

 

Exception Table Attribute Generation

To generate exception table, three pseudo-instructions are used.

    try TRAP_IDENT

        Starts trap range

    endtry TRAP_IDENT

        Ends trap range

    catch TRAP_IDENT CONSTANT_CELL(class)

        Starts exception handler.

TRAP_IDENT represents the name or number of an exception table entry. CONSTANT_CELL in "catch" pseudo_instruction means catch type. Each exception table entry contains 4 values:start-pc, end-pc, catch-pc, catch-type. In jasm, each entry is denoted with some (local) identifier, as an example: TRAP_IDENT.

To set start-pc, place "try TRAP_IDENT" before the instruction with the desirable program counter. Similarly, use "endtry TRAP_IDENT" for end-pc and "catch TRAP_IDENT, catch-type" for catch-pc and catch-type (which is usually a constant pool reference). Try, endtry, and catch pseudoinstructions may be placed in any order. The order of entries in exception table is significant (see JVM specification). However, the only way to control this order is to place catch-clauses in appropriate textual order: assembler adds an entry in the exception table each time it encounters a catch-clause.

Example:

    try {
	     try {
		 	throw new Exception("EXC");
	     } catch (NullPointerException e){
		 	throw e;
	     } catch (Exception e){
		 	throw e;
	     }
	 } catch (Throwable e){
		 throw e;
	 }

 

will be coded in assembler as follows:

try R1, R2; // single "try" or "endtry" can start several regions
		new	class java/lang/Exception;
		dup;
		ldc	String "EXC";
		invokespecial java/lang/Exception.<init>:"(Ljava/lang/String;)V";
		athrow;
 endtry R1;
 catch R1 java/lang/NullPointerException; // only one "catch" per entry allowed   
		astore_1;
		aload_1;
		athrow;
 catch R1 java/lang/Exception; // same region (R1) can appear in different catches
		astore_1;
		aload_1;
		athrow;
 endtry R2;
 catch R2 java/lang/Throwable;
		astore_1;
		aload_1;
		athrow;

 

StackMap Table Attribute Generation

Stack Maps are denoted by the pseudo-op opcode stack_map, and they can be identified by three basic items:

stackMap_Item_MapType = (bogus | int | float | double | long | null | this | CP)  
 
 stackMap_Item_Object = CONSTANT_CELL_CLASS 
 stackMap_Item_NewObject = at LABEL 

All stack_map directives are collected by the assembler, and are used to create a StackMap Table attribute.

Example 1 (MapType):

public Method "<init>":"()V"
    stack 1 locals 1
{
        aload_0;
        invokespecial    Method java/lang/Object."<init>":"()V";
        return;
        stack_frame_type full;

        stack_map bogus;
        ...
}

Example 2 (Object):

public Method "<init>":"()V"
    stack 2 locals 1
{
        ...
        stack_map class java/lang/Object;
        nop;
        return;
}

Example 3 (NewObject):

public Method "<init>":"()V"
    stack 2 locals 1
{
        ...
        stack_map at L5;
        nop;
        return;
}

StackFrameType Table Attribute Generation

StackFrameTypes are similar assembler directives as StackMap. These directives can appear anywhere in the code, and the assembler will collect them to produce a StackFrameType attribute.

frame_type = ( same | stack1 | stack1_ex | chop1 | chop2 | chop3 | 
               same_ex | append | full ) 

Example 1 (full stack frame type):

 

public Method "<init>":"()V"
    stack 1 locals 1
{
        aload_0;
        invokespecial    Method java/lang/Object."<init>":"()V";
        return;
        stack_frame_type full;
        stack_map bogus;
        ...
}

 

Example 2 (append, chop2, and same stack frame types):

 

public Method foo:"(Z)V"
	stack 2 locals 5
{
        ...
		iload_2;
		iconst_2;
		if_icmpge	L30;

 L27: stack_frame_type append;
		locals_map int, int;
		iconst_2;
		istore	4;

 L30: stack_frame_type chop2;
		goto	L9;

 L33: stack_frame_type same;
		getstatic	Field java/lang/System.out:"Ljava/io/PrintStream;";
		ldc	String "Chop2 attribute test";
		invokevirtual	Method java/io/PrintStream.println:"(Ljava/lang/String;)V";
		return;
        ...
}

 

LocalsMap Table

Locals Maps are typically associated with a stack_frame_type, and are accumulated per stack frame. They typically follow a stack_frame_type directive.

locals_type = stackMap_Item_MapType | CONSTANT_CELL_CLASS  

Example (a locals map specifying 2 ints):

 

public Method foo:"(Z)V"
	stack 2 locals 5
{
        ...
		iload_2;
		iconst_2;
		if_icmpge	L30;
	L27:	stack_frame_type append;

 locals_map int, int;
		iconst_2;
		istore	4;
	L30:	stack_frame_type chop2;
		goto	L9;
	L33:	stack_frame_type same;
		getstatic	Field java/lang/System.out:"Ljava/io/PrintStream;";
		ldc	String "Chop2 attribute test";
		invokevirtual	Method java/io/PrintStream.println:"(Ljava/lang/String;)V";
		return;
        ...
}

Inner-Class Declarations

INNER_CLASS_DECLARATIONS: list of

    INNER_CLASS_DECLARATION

INNER_CLASS_DECLARATION:

    INNER_CLASS_ACCESS InnerClass [INNER_CLASS_NAME=]? INNER_CLASS_INFO [of OUTER_CLASS_INFO]? ;

INNER_CLASS_NAME:

    IDENT | CPX_name

INNER_CLASS_INFO:

    CONSTANT_CELL(class)  

OUTER_CLASS_INFO:

    CONSTANT_CELL(class)

INNER_CLASS_ACCESS: list of

    [public|protected|private][static][final][interface][abstract]
[synthetic][annotation][enum]

Example:

    InnerClass InCl=class test$InCl of class test;

Annotation Declarations

Member Annotations

Member annotations are a subset of the basic annotations support provided in JDK 5.0 (1.5). These are annotations that ornament Packages, Classes, and Members either visibly (accessible at runtime) or invisibly (not accessible at runtime). In JASM, visible annotations are denoted by the token @, while invisible annotations are denoted by the token @-.

Synopsis

ANNOTATIONS:

    [ANNOTATION_DECLARATION]+;

ANNOTATION_DECLARATION:

    @+|@- ANNOTATION_NAME [ANNOTATION_VALUE_DECLARATIONS]

 

The '@+' token identifies a Runtime Visible Annotation, where the '@-' token identifies a Runtime Invisible Annotation.

 

ANNOTATION_NAME:

    IDENT

ANNOTATION_VALUE_DECLARATIONS: list of (comma separated)

    ANNOTATION_VALUE_DECLARATION

ANNOTATION_VALUE_DECLARATION:

    [ANNOTATION_VALUE_IDENT=] [ANNOTATION_VALUE]

ANNOTATION_VALUE_IDENT:

    IDENT

ANNOTATION_VALUE:

    ANNOTATION_VALUE_PRIMITIVE | Array of ANNOTATION_VALUE_PRIMITIVE

ANNOTATION_VALUE_PRIMITIVE:

    PRIMITIVE_TYPE | STRING | CLASS | ENUM | ANNOTATION_DECLARATION

CLASS:

    class CONSTANT_CELL(class)

ENUM:

    enum CONSTANT_CELL(class) CONSTANT_CELL(string) (where string is Enum type name)

PRIMITIVE_TYPE:

    BOOLEAN | BYTE | CHAR | SHORT | INTEGER | LONG | FLOAT | DOUBLE 

The '@+' token identifies a Runtime Visible Annotation, where the '@-' token identifies a Runtime Invisible Annotation.

Note
    Types (Boolean, Byte, Char, and Short) are normalized into Integer's within the constant pool.
    Annotation values with these types may be identified with a keyword in front of an integer value.

     eg.       boolean true (or: boolean 1)
                 byte 20
                 char 97
                 short 2130

    Other primitive types are parsed according to normal prefix and suffix conventions
    (eg. Double = xxx.xd, Float = xxx.xf, Long = xxxL). 
    Strings are identified and delimited by '"' (quotation marks).

   Keywords 'class' and 'enum' identify those annotation types explicitly. Values within classes and enums may
   either be identifiers (strings) or Constant Pool IDs.

   Annotations specified as the value of an Annotation field are identified by the JASM annotation keywords '@+' and '@-'.

   Arrays are delimited by '{' and '}' marks, with individual elements delimited by ',' (comma).

Examples

Example 1 (Class Annotation, Visible)

 

@+ClassPreamble { 
     author = "John Doe", 
     date = "3/17/2002", 
     currentRevision = 6, 
     lastModified = "4/12/2004", 
     lastModifiedBy = "Jane Doe", 
     reviewers = {
        "Alice",
        "Bob",
        "Cindy"}
}

super public class MyClass
	version 50:0
{
 ...

 

Example 2 (Field Annotation, Invisible)

@-FieldPreamble {
     author = "Mustafa", 
     date = "3/17/2009", 
     currentRevision = 4
}
Field foo:I;

...

Example 3 (Field Annotation, All subtypes)

@+FieldPreamble { 
	boolAnnot      = boolean 1, 					// Boolean
	charBear       = char 97, 					// Char
	sharkByte      = byte 17, 					// Byte
	shortCircuit   = short 4386,					// Short 
	integerHead    = 42,						// Int 
	longJohnSilver = 55l,						// Long 
	floatBoat      = 1.0f,						// Float 
	doubleDip      = 10.0d,						// Double 
	stringBeans    = "foo",						// String 
	severity       = enum FieldPreamble$Severity IMPORTANT,   	// Enum
	classAnnot     = class FieldPreamble$FooBall,			// Class
	tm = @+Trademark { description = "embedded", owner = "ktl"}	// Annotation
}
Field foo:I;

...

Note:
 JASM does not enforce the annotation value declarations like a compiler would.  It only checks to see that an annotation structure is well-formed.

Type Annotations

Member annotations are a subset of the basic annotations support provided in JDK 7.0 (1.7). These are annotations that ornament Packages, Classes, and Members either visibly (accessible at runtime) or invisibly (not accessible at runtime). In JASM, visible annotations are denoted by the token @T+, while invisible annotations are denoted by the token @T-.

Synopsis

TYPE_ANNOTATION_DECLARATION:@T+|@T- ANNOTATION_NAME [TYPE_ANNOTATION_VALUE_DECLARATIONS]

TYPE_ANNOTATION_VALUE_DECLARATIONS: list of (comma separated)
TYPE_ANNOTATION_VALUE_DECLARATION

TYPE_ANNOTATION_VALUE_DECLARATION:{ { ANNOTATION_VALUE_DECLARATION+ } TARGET PATH }

TARGET:{ TARGET_TYPE TARGET_INFO }


TARGET_TYPE:
         


TARGET_TYPE:	TARGET_INFO_TYPE:
CLASS_TYPE_PARAMETER	TYPEPARAM
METHOD_TYPE_PARAMETER	TYPEPARAM
CLASS_EXTENDS	SUPERTYPE
CLASS_TYPE_PARAMETER_BOUND	TYPEPARAM_BOUND
METHOD_TYPE_PARAMETER_BOUND	TYPEPARAM_BOUND
FIELD	EMPTY
METHOD_RETURN	EMPTY|
METHOD_RECEIVER	EMPTY
METHOD_FORMAL_PARAMETER	METHODPARAM
THROWS	EXCEPTION
LOCAL_VARIABLE	LOCALVAR
RESOURCE_VARIABLE	LOCALVAR
EXCEPTION_PARAM	CATCH
INSTANCEOF	OFFSET
NEW	OFFSET
CONSTRUCTOR_REFERE CE_RECEIVER	OFFSET
METHOD_REFERENCE_RECEIVER	OFFSET
CAST	TYPEARG
CONSTRUCTOR_INVOCATION_TYPE_ARGUMENT	TYPEARG
METHOD_INVOCATION_TYPE_ARGUMENT	TYPEARG
CONSTRUCTOR_REFERENCE_TYPE_ARGUMENT	TYPEARG
METHOD_REFERENCE_TYPE_ARGUMENT	TYPEARG

 

TARGET_INFO_TYPE: TYPEPARAM | SUPERTYPE | TYPEPARAM_BOUND | EMPTY | METHODPARAM | EXCEPTION | LOCALVAR | CATCH | OFFSET |  TYPEARG
TYPEPARAM:
paramIndex(INTEGER)


SUPERTYPE:
typeIndex(INTEGER)typeIndex(INTEGER)

TYPEPARAM_BOUND:
paramIndex(INTEGER) boundIndex(INTEGER)


EMPTY: 


METHODPARAM:
index(paramIndex(INTEGER)
EXCEPTION:
typeIndex(INTEGER) 


LOCALVAR:
{ LVENTRY }+numEntries

LVENTRY:
startpc(INTEGER) length(INTEGER) index(INTEGER) 

offset(INTEGER)
TYPEARG:
offset(INTEGER) typeIndex(INTEGER)


PATH: list of (space separated)
{ PATH_ENTRY+ }
{ PATH_KIND PATH_INDEX }


PATH_KIND: ARRAY | INNER_TYPE | WILDCARD | TYPE_ARGUMENT
 
PATH_INDEX: 
 INTEGER 
 

Parameter Names and Parameter Annotations

Parameter annotations are another subset of the basic annotations support provided in JDK 5.0 (1.5). These are annotations that ornament Parameters to methods either visibly (accessible at runtime) or invisibly (not accessible at runtime). In JASM, visible parameter annotations are denoted by the token @+, while invisible parameter annotations are denoted by the token @-.

Parameter names come from an attribute introduced in JDK 8.0 (1.8).  These are fixed parameter names that are used to ornament parameters on methods.  In Jasm, parameter names are identified by the token # followed by { } braclets

Synopsis

 

METHOD DECLARATION:

    MODIFIERS Method METHOD_NAME:"METHOD_SIGNATURE" [STACK_DECL] [LOCALS_DECL] [PARAMETERS_DECL] {[CODE]}

PARAMETERS_DECL:

    [PARAMETER_DECL]N (where N < number of params in method, each N is a unique param number)

PARAMETER_DECL:

    PARAM_NUM : [PARAM_NAME_DECL] [ANNOTATION_DECLARATIONS]

PARAM_NAME_DECL:

    #{ name PARAM_ACCESS}

PARAM_ACCESS: list of

    [final][synthetic][mandated]

 

Examples

Example 1 (Parameter Annotation)
Java Code

 

public class MyClass2 {
	
 ...

    public int doSomething(
	@VisParamPreamble ( author = "gummy" )  @InVisParamPreamble ( author = "bears" )  int barber,
	boolean of, 
        @VisParamPreamble ( author = "sour" )  @InVisParamPreamble ( author = "worms" )    int seville,
        @InVisParamPreamble1 ( reviewers = {"Dilbert", "Garfield"} ) boolean pastrami) { 
         ...
    }
 ...
}

JASM Code

Note:  The first two parameters are named ('P0'- 'P3').  Since this is a compiler controlled option, there is no way to specify parameter naming in Java source.

 

super public class MyClass2
	version 50:0
{
 ...

  public Method doSomething:"(IZIZ)I"
	stack 2 locals 5

	0: #{P0 mandated} @+VisParamPreamble { author = "gummy" } @-InVisParamPreamble { author = "bears" } 
	1: #{P1 final synthetic mandated}
        2: #{P2 mandated} @+VisParamPreamble { author = "sour" } @-InVisParamPreamble { author = "worms" } 
	3: #{P3 mandated} @-InVisParamPreamble1 { reviewers = {  "Dilbert",  "Garfield"} } 
   {
	...
   }

} // end Class MyClass2

 

Default Annotations

  Default annotations are another subset of the basic annotations support provided in JDK 5.0 (1.5). These are annotations that ornament Annotations either visibly (accessible at runtime) or invisibly (not accessible at runtime). Default annotations specify a default value for a given annotation field.

Synopsis

 

ANNOTATION INTERFACE DECLARATION:

    @interface ANNOTATION_NAME { ANNOTATION_FIELD_DECL+ }

ANNOTATION_FIELD_DECL:

    ANNOT_FIELD_TYPE ANNOTATION_NAME [ANNOTATION_DEFAULT_VALUE_DECL];

ANNOTATION_DEFAULT_VALUE_DECL:

    default ANNOTATION_VALUE (where value must be of the type ANNOT_FIELD_TYPE)

Examples

Example 1 (Default Annotation)
Java Code

 

import java.lang.annotation.*; 

@Retention(RetentionPolicy.RUNTIME)

@interface Meth2Preamble {
   String author() default "John Steinbeck";
}

JASM Code

 

interface  Meth2Preamble
    implements java/lang/annotation/Annotation
    version 50:0

{
   public abstract Method author:"()Ljava/lang/String;" default { "John Steinbeck" } ;
} // end Class Meth2Preamble

 

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PicoJava Instructions

These instructions takes 2 bytes: prefix (254 for non-privileged variant and 255 for privileged) and the opcode itself. These instructions can be coded in assembler in 2 ways: as single mnemocode identical to the description or using "priv" and "nonpriv" instructions followed with an integer representing the opcode.

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Appendix B

 

 

 

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