com.github.taomus.org.objectweb.asm.util

Class CheckClassAdapter

java.lang.Object

com.github.taomus.org.objectweb.asm.ClassVisitor

com.github.taomus.org.objectweb.asm.util.CheckClassAdapter

public class CheckClassAdapter
extends ClassVisitor

A ClassVisitor that checks that its methods are properly used. More precisely this class adapter checks each method call individually, based only on its arguments, but does not check the sequence of method calls. For example, the invalid sequence visitField(ACC_PUBLIC, "i", "I", null) visitField(ACC_PUBLIC, "i", "D", null) will not be detected by this class adapter.

CheckClassAdapter can be also used to verify bytecode transformations in order to make sure transformed bytecode is sane. For example:

   InputStream is = ...; // get bytes for the source class
   ClassReader cr = new ClassReader(is);
   ClassWriter cw = new ClassWriter(cr, ClassWriter.COMPUTE_MAXS);
   ClassVisitor cv = new MyClassAdapter(new CheckClassAdapter(cw));
   cr.accept(cv, 0);
 
   StringWriter sw = new StringWriter();
   PrintWriter pw = new PrintWriter(sw);
   CheckClassAdapter.verify(new ClassReader(cw.toByteArray()), false, pw);
   assertTrue(sw.toString(), sw.toString().length()==0);
 

Above code runs transformed bytecode trough the CheckClassAdapter. It won't be exactly the same verification as JVM does, but it run data flow analysis for the code of each method and checks that expectations are met for each method instruction.

If method bytecode has errors, assertion text will show the erroneous instruction number and dump of the failed method with information about locals and stack slot for each instruction. For example (format is - insnNumber locals : stack):

 org.objectweb.asm.tree.analysis.AnalyzerException: Error at instruction 71: Expected I, but found .
   at org.objectweb.asm.tree.analysis.Analyzer.analyze(Analyzer.java:289)
   at org.objectweb.asm.util.CheckClassAdapter.verify(CheckClassAdapter.java:135)
 ...
 remove()V
 00000 LinkedBlockingQueue$Itr . . . . . . . .  :
   ICONST_0
 00001 LinkedBlockingQueue$Itr . . . . . . . .  : I
   ISTORE 2
 00001 LinkedBlockingQueue$Itr . I . . . . . .  :
 ...
 
 00071 LinkedBlockingQueue$Itr . I . . . . . .  :
   ILOAD 1
 00072 ?
   INVOKESPECIAL java/lang/Integer.<init> (I)V
 ...
 

In the above output you can see that variable 1 loaded by ILOAD 1 instruction at position 00071 is not initialized. You can also see that at the beginning of the method (code inserted by the transformation) variable 2 is initialized.

Note that when used like that, CheckClassAdapter.verify() can trigger additional class loading, because it is using SimpleVerifier.

Author:

Eric Bruneton

Field Summary

Fields inherited from class com.github.taomus.org.objectweb.asm.ClassVisitor

api, cv

Constructor Summary

Constructors

Modifier	Constructor and Description
	CheckClassAdapter(ClassVisitor cv) Constructs a new CheckClassAdapter.
	CheckClassAdapter(ClassVisitor cv, boolean checkDataFlow) Constructs a new CheckClassAdapter.
protected	CheckClassAdapter(int api, ClassVisitor cv, boolean checkDataFlow) Constructs a new CheckClassAdapter.

Method Summary

Modifier and Type	Method and Description
static void	checkClassSignature(java.lang.String signature) Checks a class signature.
static void	checkFieldSignature(java.lang.String signature) Checks a field signature.
static void	checkMethodSignature(java.lang.String signature) Checks a method signature.
static void	main(java.lang.String[] args) Checks a given class.
static void	verify(ClassReader cr, boolean dump, java.io.PrintWriter pw) Checks a given class
static void	verify(ClassReader cr, java.lang.ClassLoader loader, boolean dump, java.io.PrintWriter pw) Checks a given class.
void	visit(int version, int access, java.lang.String name, java.lang.String signature, java.lang.String superName, java.lang.String[] interfaces) Visits the header of the class.
AnnotationVisitor	visitAnnotation(java.lang.String desc, boolean visible) Visits an annotation of the class.
void	visitAttribute(Attribute attr) Visits a non standard attribute of the class.
void	visitEnd() Visits the end of the class.
FieldVisitor	visitField(int access, java.lang.String name, java.lang.String desc, java.lang.String signature, java.lang.Object value) Visits a field of the class.
void	visitInnerClass(java.lang.String name, java.lang.String outerName, java.lang.String innerName, int access) Visits information about an inner class.
MethodVisitor	visitMethod(int access, java.lang.String name, java.lang.String desc, java.lang.String signature, java.lang.String[] exceptions) Visits a method of the class.
void	visitOuterClass(java.lang.String owner, java.lang.String name, java.lang.String desc) Visits the enclosing class of the class.
void	visitSource(java.lang.String file, java.lang.String debug) Visits the source of the class.
AnnotationVisitor	visitTypeAnnotation(int typeRef, TypePath typePath, java.lang.String desc, boolean visible) Visits an annotation on a type in the class signature.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

CheckClassAdapter

public CheckClassAdapter(ClassVisitor cv)

Constructs a new CheckClassAdapter. Subclasses must not use this constructor. Instead, they must use the CheckClassAdapter(int, ClassVisitor, boolean) version.

Parameters:

cv - the class visitor to which this adapter must delegate calls.

CheckClassAdapter

public CheckClassAdapter(ClassVisitor cv,
                         boolean checkDataFlow)

Constructs a new CheckClassAdapter. Subclasses must not use this constructor. Instead, they must use the CheckClassAdapter(int, ClassVisitor, boolean) version.

Parameters:

cv - the class visitor to which this adapter must delegate calls.

checkDataFlow - true to perform basic data flow checks, or false to not perform any data flow check (see CheckMethodAdapter). This option requires valid maxLocals and maxStack values.

Throws:

java.lang.IllegalStateException - If a subclass calls this constructor.

CheckClassAdapter

protected CheckClassAdapter(int api,
                            ClassVisitor cv,
                            boolean checkDataFlow)

Constructs a new CheckClassAdapter.

Parameters:

api - the ASM API version implemented by this visitor. Must be one of Opcodes.ASM4 or Opcodes.ASM5.

cv - the class visitor to which this adapter must delegate calls.

checkDataFlow - true to perform basic data flow checks, or false to not perform any data flow check (see CheckMethodAdapter). This option requires valid maxLocals and maxStack values.

Method Detail

main

public static void main(java.lang.String[] args)
                 throws java.lang.Exception

Checks a given class.

Usage: CheckClassAdapter <binary class name or class file name>

Parameters:

args - the command line arguments.

Throws:

java.lang.Exception - if the class cannot be found, or if an IO exception occurs.

verify

public static void verify(ClassReader cr,
                          java.lang.ClassLoader loader,
                          boolean dump,
                          java.io.PrintWriter pw)

Checks a given class.

Parameters:

cr - a ClassReader that contains bytecode for the analysis.

loader - a ClassLoader which will be used to load referenced classes. This is useful if you are verifiying multiple interdependent classes.

dump - true if bytecode should be printed out not only when errors are found.

pw - write where results going to be printed

verify

public static void verify(ClassReader cr,
                          boolean dump,
                          java.io.PrintWriter pw)

Checks a given class

Parameters:

cr - a ClassReader that contains bytecode for the analysis.

dump - true if bytecode should be printed out not only when errors are found.

pw - write where results going to be printed

visit

public void visit(int version,
                  int access,
                  java.lang.String name,
                  java.lang.String signature,
                  java.lang.String superName,
                  java.lang.String[] interfaces)

Description copied from class: ClassVisitor

Visits the header of the class.

Overrides:

visit in class ClassVisitor

Parameters:

version - the class version.

access - the class's access flags (see Opcodes). This parameter also indicates if the class is deprecated.

name - the internal name of the class (see getInternalName).

signature - the signature of this class. May be null if the class is not a generic one, and does not extend or implement generic classes or interfaces.

superName - the internal of name of the super class (see getInternalName). For interfaces, the super class is Object. May be null, but only for the Object class.

interfaces - the internal names of the class's interfaces (see getInternalName). May be null.

visitSource

public void visitSource(java.lang.String file,
                        java.lang.String debug)

Description copied from class: ClassVisitor

Visits the source of the class.

Overrides:

visitSource in class ClassVisitor

Parameters:

file - the name of the source file from which the class was compiled. May be null.

debug - additional debug information to compute the correspondance between source and compiled elements of the class. May be null.

visitOuterClass

public void visitOuterClass(java.lang.String owner,
                            java.lang.String name,
                            java.lang.String desc)

Description copied from class: ClassVisitor

Visits the enclosing class of the class. This method must be called only if the class has an enclosing class.

Overrides:

visitOuterClass in class ClassVisitor

Parameters:

owner - internal name of the enclosing class of the class.

name - the name of the method that contains the class, or null if the class is not enclosed in a method of its enclosing class.

desc - the descriptor of the method that contains the class, or null if the class is not enclosed in a method of its enclosing class.

visitInnerClass

public void visitInnerClass(java.lang.String name,
                            java.lang.String outerName,
                            java.lang.String innerName,
                            int access)

Description copied from class: ClassVisitor

Visits information about an inner class. This inner class is not necessarily a member of the class being visited.

Overrides:

visitInnerClass in class ClassVisitor

Parameters:

name - the internal name of an inner class (see getInternalName).

outerName - the internal name of the class to which the inner class belongs (see getInternalName). May be null for not member classes.

innerName - the (simple) name of the inner class inside its enclosing class. May be null for anonymous inner classes.

access - the access flags of the inner class as originally declared in the enclosing class.

visitField

public FieldVisitor visitField(int access,
                               java.lang.String name,
                               java.lang.String desc,
                               java.lang.String signature,
                               java.lang.Object value)

Description copied from class: ClassVisitor

Visits a field of the class.

Overrides:

visitField in class ClassVisitor

Parameters:

access - the field's access flags (see Opcodes). This parameter also indicates if the field is synthetic and/or deprecated.

name - the field's name.

desc - the field's descriptor (see Type).

signature - the field's signature. May be null if the field's type does not use generic types.

value - the field's initial value. This parameter, which may be null if the field does not have an initial value, must be an Integer, a Float, a Long, a Double or a String (for int, float, long or String fields respectively). This parameter is only used for static fields. Its value is ignored for non static fields, which must be initialized through bytecode instructions in constructors or methods.

Returns:

a visitor to visit field annotations and attributes, or null if this class visitor is not interested in visiting these annotations and attributes.

visitMethod

public MethodVisitor visitMethod(int access,
                                 java.lang.String name,
                                 java.lang.String desc,
                                 java.lang.String signature,
                                 java.lang.String[] exceptions)

Description copied from class: ClassVisitor

Visits a method of the class. This method must return a new MethodVisitor instance (or null) each time it is called, i.e., it should not return a previously returned visitor.

Overrides:

visitMethod in class ClassVisitor

Parameters:

access - the method's access flags (see Opcodes). This parameter also indicates if the method is synthetic and/or deprecated.

name - the method's name.

desc - the method's descriptor (see Type).

signature - the method's signature. May be null if the method parameters, return type and exceptions do not use generic types.

exceptions - the internal names of the method's exception classes (see getInternalName). May be null.

Returns:

an object to visit the byte code of the method, or null if this class visitor is not interested in visiting the code of this method.

visitAnnotation

public AnnotationVisitor visitAnnotation(java.lang.String desc,
                                         boolean visible)

Description copied from class: ClassVisitor

Visits an annotation of the class.

Overrides:

visitAnnotation in class ClassVisitor

Parameters:

desc - the class descriptor of the annotation class.

visible - true if the annotation is visible at runtime.

Returns:

a visitor to visit the annotation values, or null if this visitor is not interested in visiting this annotation.

visitTypeAnnotation

public AnnotationVisitor visitTypeAnnotation(int typeRef,
                                             TypePath typePath,
                                             java.lang.String desc,
                                             boolean visible)

Description copied from class: ClassVisitor

Visits an annotation on a type in the class signature.

Overrides:

visitTypeAnnotation in class ClassVisitor

Parameters:

typeRef - a reference to the annotated type. The sort of this type reference must be CLASS_TYPE_PARAMETER, CLASS_TYPE_PARAMETER_BOUND or CLASS_EXTENDS. See TypeReference.

typePath - the path to the annotated type argument, wildcard bound, array element type, or static inner type within 'typeRef'. May be null if the annotation targets 'typeRef' as a whole.

desc - the class descriptor of the annotation class.

visible - true if the annotation is visible at runtime.

Returns:

a visitor to visit the annotation values, or null if this visitor is not interested in visiting this annotation.

visitAttribute

public void visitAttribute(Attribute attr)

Description copied from class: ClassVisitor

Visits a non standard attribute of the class.

Overrides:

visitAttribute in class ClassVisitor

Parameters:

attr - an attribute.

visitEnd

public void visitEnd()

Description copied from class: ClassVisitor

Visits the end of the class. This method, which is the last one to be called, is used to inform the visitor that all the fields and methods of the class have been visited.

Overrides:

visitEnd in class ClassVisitor

checkClassSignature

public static void checkClassSignature(java.lang.String signature)

Checks a class signature.

Parameters:

signature - a string containing the signature that must be checked.

checkMethodSignature

public static void checkMethodSignature(java.lang.String signature)

Checks a method signature.

Parameters:

signature - a string containing the signature that must be checked.

checkFieldSignature

public static void checkFieldSignature(java.lang.String signature)

Checks a field signature.

Parameters:

signature - a string containing the signature that must be checked.