org.objectweb.asm.util
public class CheckClassAdapter extends ClassAdapter
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.In the above output you can see that variable 1 loaded by(I)V ...
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
.
Constructor Summary | |
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CheckClassAdapter(ClassVisitor cv)
Constructs a new CheckClassAdapter.
| |
CheckClassAdapter(ClassVisitor cv, boolean checkDataFlow)
Constructs a new CheckClassAdapter.
|
Method Summary | |
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static void | main(String[] args)
Checks a given class. |
static void | verify(ClassReader cr, ClassLoader loader, boolean dump, PrintWriter pw)
Checks a given class
|
static void | verify(ClassReader cr, boolean dump, PrintWriter pw)
Checks a given class
|
void | visit(int version, int access, String name, String signature, String superName, String[] interfaces) |
AnnotationVisitor | visitAnnotation(String desc, boolean visible) |
void | visitAttribute(Attribute attr) |
void | visitEnd() |
FieldVisitor | visitField(int access, String name, String desc, String signature, Object value) |
void | visitInnerClass(String name, String outerName, String innerName, int access) |
MethodVisitor | visitMethod(int access, String name, String desc, String signature, String[] exceptions) |
void | visitOuterClass(String owner, String name, String desc) |
void | visitSource(String file, String debug) |
Parameters: cv the class visitor to which this adapter must delegate calls.
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).
Usage: CheckClassAdapter <fully qualified class name or class file name>
Parameters: args the command line arguments.
Throws: Exception if the class cannot be found, or if an IO exception occurs.
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
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