I am trying bcel to modify a method by inserting invoke before specific instructions.
It seems that my instrumentation would result in a different stackmap table, which can not be auto-generated by the bcel package itself.
So, my instrumented class file contains the old stackmap table, which would cause error with jvm.
I haved tried with removeCodeAttributes, the method of MethodGen, that can remove all the code attributes. It can work in simple cases, a wrapped function, for example. And it can not work in my case now.
public class Insert{
public static void main(String[] args) throws ClassFormatException, IOException{
Insert isrt = new Insert();
String className = "StringBuilder.class";
JavaClass jclzz = new ClassParser(className).parse();
ClassGen cgen = new ClassGen(jclzz);
ConstantPoolGen cpgen = cgen.getConstantPool();
MethodGen mgen = new MethodGen(jclzz.getMethods()[1], className, cpgen);
InstructionFactory ifac = new InstructionFactory(cgen);
InstructionList ilist = mgen.getInstructionList();
for (InstructionHandle ihandle : ilist.getInstructionHandles()){
System.out.println(ihandle.toString());
}
InstructionFinder f = new InstructionFinder(ilist);
InstructionHandle[] insert_pos = (InstructionHandle[])(f.search("invokevirtual").next());
Instruction inserted_inst = ifac.createInvoke("java.lang.System", "currentTimeMillis", Type.LONG, Type.NO_ARGS, Constants.INVOKESTATIC);
System.out.println(inserted_inst.toString());
ilist.insert(insert_pos[0], inserted_inst);
mgen.setMaxStack();
mgen.setMaxLocals();
mgen.removeCodeAttributes();
cgen.replaceMethod(jclzz.getMethods()[1], mgen.getMethod());
ilist.dispose();
//output the file
FileOutputStream fos = new FileOutputStream(className);
cgen.getJavaClass().dump(fos);
fos.close();
}
}
Removing a StackMapTable is not a proper solution for fixing a wrong StackMapTable. The important cite is:
4.7.4. The StackMapTable Attribute
In a class file whose version number is 50.0 or above, if a method's Code attribute does not have a StackMapTable attribute, it has an implicit stack map attribute (§4.10.1). This implicit stack map attribute is equivalent to a StackMapTable attribute with number_of_entries equal to zero.
Since a StackMapTable must have explicit entries for every branch target, such an implicit StackMapTable will work with branch-free methods only. But in these cases, the method usually doesn’t have an explicit StackMapTable anyway, so you wouldn’t have that problem then (unless the method had branches which your instrumentation removed).
Another conclusion is that you can get away with removing the StackMapTable, if you patch the class file version number to a value below 50. Of course, this is only a solution if you don’t need any class file feature introduced in version 50 or newer…
There was a grace period in which JVMs supported a fall-back mode for class files with broken StackMapTables just for scenarios like yours, where the tool support is not up-to-date. (See -XX:+FailoverToOldVerifier or -XX:-UseSplitVerifier) But the grace period is over now and that support has been declined, i.e. Java 8 JVMs do not support the fall-back mode anymore.
If you want to keep up with the Java development and instrument newer class files which might use features of these new versions you have only two choices:
Calculate the correct StackMapTable manually
Use a tool which supports calculating the correct StackMapTable attributes, e.g. ASM, (see java-bytecode-asm) does support it
Related
At this moment I participate in big legacy project with many huge classes and generated code.
I wish to find all methods that have bytecode length bigger than 8000 bytes (because OOTB java will not optimize it).
I found manual way like this: How many bytes of bytecode has a particular method in Java?
, however my goal is to scan many files automatically.
I tried to use jboss-javassist, but AFAIK getting bytecode length is available only on class level.
Huge methods might indeed never get inlined, however, but I have my doubts regarding the threshold of 8000. This comment suggests a much smaller limit, though it is platform and configuration dependent anyway.
You are right that getting bytecode length needs to process classes on that low level, however, you didn’t specify what actual obstacle you encountered when trying to do that with Javassist. A simple program doing that with Javassist, would be
try(InputStream is=javax.swing.JComponent.class.getResourceAsStream("JComponent.class")) {
ClassFile cf = new ClassFile(new DataInputStream(is));
for(MethodInfo mi: cf.getMethods()) {
CodeAttribute ca = mi.getCodeAttribute();
if(ca == null) continue; // abstract or native
int bLen = ca.getCode().length;
if(bLen > 300)
System.out.println(mi.getName()+" "+mi.getDescriptor()+", "+bLen+" bytes");
}
}
This has been written and tested with a recent version of Javassist that uses Generics in the API. If you have a different/older version, you have to use
try(InputStream is=javax.swing.JComponent.class.getResourceAsStream("JComponent.class")) {
ClassFile cf = new ClassFile(new DataInputStream(is));
for(Object miO: cf.getMethods()) {
MethodInfo mi = (MethodInfo)miO;
CodeAttribute ca = mi.getCodeAttribute();
if(ca == null) continue; // abstract or native
int bLen = ca.getCode().length;
if(bLen > 300)
System.out.println(mi.getName()+" "+mi.getDescriptor()+", "+bLen+" bytes");
}
}
I just started using Wala Java Slicer to do some source code analysis tasks. I have a question about the proper use of the library. Assuming I have the following example code:
public void main(String[] args) {
...
UserType ut = userType;
int i = ut.getInt();
...
System.out.println(i);
}
Calculating a slice for the println statement with Wala gives the following statements:
NORMAL_RET_CALLER:Node: < Application, LRTExecutionClass, main([Ljava/lang/String;)V > Context: Everywhere[15]13 = invokevirtual < Application, LUserType, getInt()I > 11 #27 exception:12
NORMAL main:23 = getstatic < Application, Ljava/lang/System, out, <Application,Ljava/io/PrintStream> > Node: < Application, LRTExecutionClass, main([Ljava/lang/String;)V > Context: Everywhere
NORMAL main:invokevirtual < Application, Ljava/io/PrintStream, println(I)V > 23,13 #63 exception:24 Node: < Application, LRTExecutionClass, main([Ljava/lang/String;)V > Context: Everywhere
The code I am using to create the slice with Wala is shown below:
AnalysisScope scope = AnalysisScopeReader.readJavaScope("...",
null, WalaJavaSlicer.class.getClassLoader());
ClassHierarchy cha = ClassHierarchy.make(scope);
Iterable<Entrypoint> entrypoints = Util.makeMainEntrypoints(scope, cha);
AnalysisOptions options = new AnalysisOptions(scope, entrypoints);
// Build the call graph
CallGraphBuilder cgb = Util.makeZeroCFABuilder(options, new AnalysisCache(),cha, scope, null, null);
CallGraph cg = cgb.makeCallGraph(options, null);
PointerAnalysis pa = cgb.getPointerAnalysis();
// Find seed statement
Statement statement = findCallTo(findMainMethod(cg), "println");
// Context-sensitive thin slice
Collection<Statement> slice = Slicer.computeBackwardSlice(statement, cg, pa, DataDependenceOptions.NO_BASE_NO_HEAP, ControlDependenceOptions.NONE);
dumpSlice(slice);
There are a number of statements that I expect to find in the slice but are not present:
The assign statement ut = userType is not included even though the dependent method call ut.getInt(), IS included in the slice
No statements from the implementation of getInt() are included. Is there an option to activate "inter-procedural" slicing? I should mention here that the .class file is included in the path used to create the AnalysisScope.
As you can see, I am using DataDependenceOptions.NO_BASE_NO_HEAP and ControlDependenceOptions.NONE for the dependence options. But even when I use FULL for both, the problem persists.
What am I doing wrong?
The assign statement ut = userType is not included even though the
dependent method call ut.getInt(), IS included in the slice
I suspect that assignment never makes it into the byte code since it's an un-required local variable and hence will not be visible to WALA:
Because the SSA IR has already been somewhat optimized, some
statements such as simple assignments (x=y, y=z) do not appear in the
IR, due to copy propagation optimizations done automatically during
SSA construction by the SSABuilder class. In fact, there is no SSA
assignment instruction; additionally, a javac compiler is free to do
these optimizations, so the statements may not even appear in the
bytecode. Thus, these Java statements will never appear in the slice.
http://wala.sourceforge.net/wiki/index.php/UserGuide:Slicer#Warning:_exclusion_of_copy_statements_from_slice
I switched an existing code base to Java 7 and I keep getting this warning:
warning: File for type '[Insert class here]' created in the last round
will not be subject to annotation processing.
A quick search reveals that no one has hit this warning.
It's not documented in the javac compiler source either:
From OpenJDK\langtools\src\share\classes\com\sun\tools\javac\processing\JavacFiler.java
private JavaFileObject createSourceOrClassFile(boolean isSourceFile, String name) throws IOException {
checkNameAndExistence(name, isSourceFile);
Location loc = (isSourceFile ? SOURCE_OUTPUT : CLASS_OUTPUT);
JavaFileObject.Kind kind = (isSourceFile ?
JavaFileObject.Kind.SOURCE :
JavaFileObject.Kind.CLASS);
JavaFileObject fileObject =
fileManager.getJavaFileForOutput(loc, name, kind, null);
checkFileReopening(fileObject, true);
if (lastRound) // <-------------------------------TRIGGERS WARNING
log.warning("proc.file.create.last.round", name);
if (isSourceFile)
aggregateGeneratedSourceNames.add(name);
else
aggregateGeneratedClassNames.add(name);
openTypeNames.add(name);
return new FilerOutputJavaFileObject(name, fileObject);
}
What does this mean and what steps can I take to clear this warning?
Thanks.
The warning
warning: File for type '[Insert class here]' created in the last round
will not be subject to annotation processing
means that your were running an annotation processor creating a new class or source file using a javax.annotation.processing.Filer implementation (provided through the javax.annotation.processing.ProcessingEnvironment) although the processing tool already decided its "in the last round".
This may be problem (and thus the warning) because the generated file itself may contain annotations being ignored by the annotation processor (because it is not going to do a further round).
The above ought to answer the first part of your question
What does this mean and what steps can I take to clear this warning?
(you figured this out already by yourself, didn't you :-))
What possible steps to take? Check your annotation processors:
1) Do you really have to use filer.createClassFile / filer.createSourceFile on the very last round of the annotaion processor? Usually one uses the filer object inside of a code block like
for (TypeElement annotation : annotations) {
...
}
(in method process). This ensures that the annotation processor will not be in its last round (the last round always being the one having an empty set of annotations).
2) If you really can't avoid writing your generated files in the last round and these files are source files, trick the annotation processor and use the method "createResource" of the filer object (take "SOURCE_OUTPUT" as location).
In OpenJDK test case this warning produced because processor uses "processingOver()" to write new file exactly at last round.
public boolean process(Set<? extends TypeElement> elems, RoundEnvironment renv) {
if (renv.processingOver()) { // Write only at last round
Filer filer = processingEnv.getFiler();
Messager messager = processingEnv.getMessager();
try {
JavaFileObject fo = filer.createSourceFile("Gen");
Writer out = fo.openWriter();
out.write("class Gen { }");
out.close();
messager.printMessage(Diagnostic.Kind.NOTE, "File 'Gen' created");
} catch (IOException e) {
messager.printMessage(Diagnostic.Kind.ERROR, e.toString());
}
}
return false;
}
I modified original example code a bit. Added diagnostic note "File 'Gen' created", replaced "*" mask with "org.junit.runner.RunWith" and set return value to "true". Produced compiler log was:
Round 1:
input files: {ProcFileCreateLastRound}
annotations: [org.junit.runner.RunWith]
last round: false
Processor AnnoProc matches [org.junit.runner.RunWith] and returns true.
Round 2:
input files: {}
annotations: []
last round: true
Note: File 'Gen' created
Compilation completed successfully with 1 warning
0 errors
1 warning
Warning: File for type 'Gen' created in the last round will not be subject to annotation processing.
If we remove my custom note from log, it's hard to tell that file 'Gen' was actually created on 'Round 2' - last round. So, basic advice applies: if in doubt - add more logs.
Where is also a little bit of useful info on this page:
http://docs.oracle.com/javase/7/docs/technotes/tools/solaris/javac.html
Read section about "ANNOTATION PROCESSING" and try to get more info with compiler options:
-XprintProcessorInfo
Print information about which annotations a processor is asked to process.
-XprintRounds Print information about initial and subsequent annotation processing rounds.
I poked around the java 7 compiler options and I found this:
-implicit:{class,none}
Controls the generation of class files for implicitly loaded source files. To automatically generate class files, use -implicit:class. To suppress class file generation, use -implicit:none. If this option is not specified, the default is to automatically generate class files. In this case, the compiler will issue a warning if any such class files are generated when also doing annotation processing. The warning will not be issued if this option is set explicitly. See Searching For Types.
Source
Can you try and implicitly declare the class file.
I am getting expected ClassVerifyErrors when attempting to load a class i have generated using ASM. On further inspection i can see that the jvm is correct and that the method is talking about has an invalid MAX_STACK value. THe strange thing is am using the auto calculate the stack and max local options so this should not be a problem...
The method with the invalid option is very simple and yet the result is bad bytecode.
I have written a class with the intended method and compared my asm generated class against what javac produces and the byte codes matchup with the only error being the max stack is 0 which is wrong while javac sets a value of 2.
Id like to avoid having to calculate tha max stack/locals myself.
Max stack and variable calculation can produce the wrong results if bytecode is not valid. You can verify that by running generated code trough the CheckClassAdapter.
For example,
ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_MAXS);
// generate code into cw instance...
PrintWriter pw = new PrintWriter(System.out);
CheckClassAdapter.verify(new ClassReader(cw.toByteArray()), true, pw);
I'm trying to validate an Atom feed with Java 5 (JRE 1.5.0 update 11). The code I have works without problem in Java 6, but fails when running in Java 5 with a
org.xml.sax.SAXParseException: src-resolve: Cannot resolve the name 'xml:base' to a(n) 'attribute declaration' component.
I think I remember reading something about the version of Xerces bundled with Java 5 having some problems with some schemas, but i cant find the workaround. Is it a known problem ? Do I have some error in my code ?
public static void validate() throws SAXException, IOException {
List<Source> schemas = new ArrayList<Source>();
schemas.add(new StreamSource(AtomValidator.class.getResourceAsStream("/atom.xsd")));
schemas.add(new StreamSource(AtomValidator.class.getResourceAsStream("/dc.xsd")));
// Lookup a factory for the W3C XML Schema language
SchemaFactory factory = SchemaFactory.newInstance("http://www.w3.org/2001/XMLSchema");
// Compile the schemas.
Schema schema = factory.newSchema(schemas.toArray(new Source[schemas.size()]));
Validator validator = schema.newValidator();
// load the file to validate
Source source = new StreamSource(AtomValidator.class.getResourceAsStream("/sample-feed.xml"));
// check the document
validator.validate(source);
}
Update : I tried the method below, but I still have the same problem if I use Xerces 2.9.0. I also tried adding xml.xsd to the list of schemas (as xml:base is defined in xml.xsd) but this time I have
Exception in thread "main" org.xml.sax.SAXParseException: schema_reference.4: Failed to read schema document 'null', because 1) could not find the document; 2) the document could not be read; 3) the root element of the document is not <xsd:schema>.
Update 2: I tried to configure a proxy with the VM arguments -Dhttp.proxyHost=<proxy.host.com> -Dhttp.proxyPort=8080 and now it works. I'll try to post a "real answer" from home.
and sorry, I cant reply as a comment : because of security reasons XHR is disabled from work ...
Indeed, people have been mentioning the Java 5 Sun provided SchemaFactory is giving troubles.
So: did you include Xerces in your project yourself?
After including Xerces, you need to ensure it is being used. If you like to hardcode it (well, as a minimal requirement you'd probably use some application properties file to enable and populate the following code):
String schemaFactoryProperty =
"javax.xml.validation.SchemaFactory:" + XMLConstants.W3C_XML_SCHEMA_NS_URI;
System.setProperty(schemaFactoryProperty,
"org.apache.xerces.jaxp.validation.XMLSchemaFactory");
SchemaFactory factory =
SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
Or, if you don't want to hardcode, or when your troublesome code would be in some 3rd party library that you cannot change, set it on the java command line or environment options. For example (on one line of course):
set JAVA_OPTS =
"-Djavax.xml.validation.SchemaFactory:http://www.w3.org/2001/XMLSchema
=org.apache.xerces.jaxp.validation.XMLSchemaFactory"
By the way: apart from the Sun included SchemaFactory implementation giving trouble (something like com.sun.org.apache.xerces.internal.jaxp.validation.xs.schemaFactoryImpl), it also seems that the "discovery" of non-JDK implementations fails in that version. If I understand correctly than, normally, just including Xerces would in fact make SchemaFactory#newInstance find that included library, and give it precedence over the Sun implementation. To my knowledge, that fails as well in Java 5, making the above configuration required.
I tried to configure a proxy with the VM arguments -Dhttp.proxyHost=<proxy.host.com> -Dhttp.proxyPort=8080 and now it works.
Ah, I didn't realize that xml.xsd is in fact the one referenced as http://www.w3.org/2001/xml.xsd or something like that. That should teach us to always show some XML and XSD fragments as well. ;-)
So, am I correct to assume that 1.) to fix the Java 5 issue, you still needed to include Xerces and set the system property, and that 2.) you did not have xml.xsd available locally?
Before you found your solution, did you happen to try using getResource rather than getResourceAsStream, to see if the exception would then have showed you some more details?
If you actually did have xml.xsd available (so: if getResource did in fact yield a URL) then I wonder what Xerces was trying to fetch from the internet then. Or maybe you did not add that schema to the list prior to adding your own schemas? The order is important: dependencies must be added first.
For whoever gets tot his question using the search: maybe using a custom EntityResolver could have indicated the source of the problem as well (if only writing something to the log and just returning null to tell Xerces to use the default behavior).
Hmmm, just read your "comment" -- editing does not alert people for new replies, so time to ask your boss for some iPhone or some other gadget that is connected to the net directly ;-)
Well, I assume you added:
schemas.add(
new StreamSource(AtomValidator.class.getResourceAsStream("/xml.xsd")));
If so, is xml.xsd actually to be found on the classpath then? I wonder if the getResourceAsStream did not yield null in your case, and how new StreamSource(null) would act then.
Even if getResourceAsStream did not yield null, the resulting StreamSource would still not know where it was loaded from, which may be a problem when trying to include references. So, what if you use the constructor StreamSource(String systemId) instead:
schemas.add(new StreamSource(AtomValidator.class.getResource("/atom.xsd")));
schemas.add(new StreamSource(AtomValidator.class.getResource("/dc.xsd")));
You might also use StreamSource(InputStream inputStream, String systemId), but I don't see any advantage over the above two lines. However, the documentation explains why passing the systemId in either of the 2 constructors seems good:
This constructor allows the systemID to be set in addition to the input stream, which allows relative URIs to be processed.
Likewise, setSystemId(String systemId) explains a bit:
The system identifier is optional if there is a byte stream or a character stream, but it is still useful to provide one, since the application can use it to resolve relative URIs and can include it in error messages and warnings (the parser will attempt to open a connection to the URI only if there is no byte stream or character stream specified).
If this doesn't work out, then maybe some custom error handler can give you more details:
ErrorHandlerImpl errorHandler = new ErrorHandlerImpl();
validator.setErrorHandler(errorHandler);
:
:
validator.validate(source);
if(errorHandler.hasErrors()){
LOG.error(errorHandler.getMessages());
throw new [..];
}
if(errorHandler.hasWarnings()){
LOG.warn(errorHandler.getMessages());
}
...using the following ErrorHandler to capture the validation errors and continue parsing as far as possible:
import org.xml.sax.helpers.DefaultHandler;
private class ErrorHandlerImpl extends DefaultHandler{
private String messages = "";
private boolean validationError = false;
private boolean validationWarning = false;
public void error(SAXParseException exception) throws SAXException{
messages += "Error: " + exception.getMessage() + "\n";
validationError = true;
}
public void fatalError(SAXParseException exception) throws SAXException{
messages += "Fatal: " + exception.getMessage();
validationError = true;
}
public void warning(SAXParseException exception) throws SAXException{
messages += "Warn: " + exception.getMessage();
validationWarning = true;
}
public boolean hasErrors(){
return validationError;
}
public boolean hasWarnings(){
return validationWarning;
}
public String getMessages(){
return messages;
}
}