001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 *  Unless required by applicable law or agreed to in writing, software
012 *  distributed under the License is distributed on an "AS IS" BASIS,
013 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 *  See the License for the specific language governing permissions and
015 *  limitations under the License.
016 *
017 */
018package org.apache.bcel.verifier.statics;
019
020
021import org.apache.bcel.Repository;
022import org.apache.bcel.classfile.ClassFormatException;
023import org.apache.bcel.classfile.JavaClass;
024import org.apache.bcel.verifier.PassVerifier;
025import org.apache.bcel.verifier.VerificationResult;
026import org.apache.bcel.verifier.Verifier;
027import org.apache.bcel.verifier.exc.LoadingException;
028import org.apache.bcel.verifier.exc.Utility;
029
030/**
031 * This PassVerifier verifies a class file according to pass 1 as
032 * described in The Java Virtual Machine Specification, 2nd edition.
033 * More detailed information is to be found at the do_verify() method's
034 * documentation.
035 *
036 * @see #do_verify()
037 */
038public final class Pass1Verifier extends PassVerifier{
039    /**
040     * DON'T USE THIS EVEN PRIVATELY! USE getJavaClass() INSTEAD.
041     * @see #getJavaClass()
042     */
043    private JavaClass jc;
044
045    /**
046     * The Verifier that created this.
047     */
048    private final Verifier myOwner;
049
050    /**
051     * Used to load in and return the myOwner-matching JavaClass object when needed.
052     * Avoids loading in a class file when it's not really needed!
053     */
054    private JavaClass getJavaClass() {
055        if (jc == null) {
056            try {
057                jc = Repository.lookupClass(myOwner.getClassName());
058            } catch (final ClassNotFoundException e) {
059                // FIXME: currently, Pass1Verifier treats jc == null as a special
060                // case, so we don't need to do anything here.  A better solution
061                // would be to simply throw the ClassNotFoundException
062                // out of this method.
063            }
064        }
065        return jc;
066    }
067
068    /**
069     * Should only be instantiated by a Verifier.
070     *
071     * @see Verifier
072     */
073    public Pass1Verifier(final Verifier owner) {
074        myOwner = owner;
075    }
076
077    /**
078     * Pass-one verification basically means loading in a class file.
079     * The Java Virtual Machine Specification is not too precise about
080     * what makes the difference between passes one and two.
081     * The answer is that only pass one is performed on a class file as
082     * long as its resolution is not requested; whereas pass two and
083     * pass three are performed during the resolution process.
084     * Only four constraints to be checked are explicitly stated by
085     * The Java Virtual Machine Specification, 2nd edition:
086     * <UL>
087     *  <LI>The first four bytes must contain the right magic number (0xCAFEBABE).
088     *  <LI>All recognized attributes must be of the proper length.
089     *  <LI>The class file must not be truncated or have extra bytes at the end.
090     *  <LI>The constant pool must not contain any superficially unrecognizable information.
091     * </UL>
092     * A more in-depth documentation of what pass one should do was written by
093     * <A HREF=mailto:pwfong@cs.sfu.ca>Philip W. L. Fong</A>:
094     * <UL>
095     *  <LI> the file should not be truncated.
096     *  <LI> the file should not have extra bytes at the end.
097     *  <LI> all variable-length structures should be well-formatted:
098     *  <UL>
099     *   <LI> there should only be constant_pool_count-1 many entries in the constant pool.
100     *   <LI> all constant pool entries should have size the same as indicated by their type tag.
101     *   <LI> there are exactly interfaces_count many entries in the interfaces array of the class file.
102     *   <LI> there are exactly fields_count many entries in the fields array of the class file.
103     *   <LI> there are exactly methods_count many entries in the methods array of the class file.
104     *   <LI> there are exactly attributes_count many entries in the attributes array of the class file,
105     *        fields, methods, and code attribute.
106     *   <LI> there should be exactly attribute_length many bytes in each attribute.
107     *        Inconsistency between attribute_length and the actually size of the attribute content should be uncovered.
108     *        For example, in an Exceptions attribute, the actual number of exceptions as required by the number_of_exceptions field
109     *        might yeild an attribute size that doesn't match the attribute_length. Such an anomaly should be detected.
110     *   <LI> all attributes should have proper length. In particular, under certain context (e.g. while parsing method_info),
111     *        recognizable attributes (e.g. "Code" attribute) should have correct format (e.g. attribute_length is 2).
112     *  </UL>
113     *  <LI> Also, certain constant values are checked for validity:
114     *  <UL>
115     *   <LI> The magic number should be 0xCAFEBABE.
116     *   <LI> The major and minor version numbers are valid.
117     *   <LI> All the constant pool type tags are recognizable.
118     *   <LI> All undocumented access flags are masked off before use. Strictly speaking, this is not really a check.
119     *   <LI> The field this_class should point to a string that represents a legal non-array class name,
120     *        and this name should be the same as the class file being loaded.
121     *   <LI> the field super_class should point to a string that represents a legal non-array class name.
122     *   <LI> Because some of the above checks require cross referencing the constant pool entries,
123     *        guards are set up to make sure that the referenced entries are of the right type and the indices
124     *        are within the legal range (0 &lt; index &lt; constant_pool_count).
125     *  </UL>
126     *  <LI> Extra checks done in pass 1:
127     *  <UL>
128     *   <LI> the constant values of static fields should have the same type as the fields.
129     *   <LI> the number of words in a parameter list does not exceed 255 and locals_max.
130     *   <LI> the name and signature of fields and methods are verified to be of legal format.
131     *  </UL>
132     * </UL>
133     * (From the Paper <A HREF="http://www.cs.sfu.ca/people/GradStudents/pwfong/personal/JVM/pass1/">
134     * The Mysterious Pass One, first draft, September 2, 1997</A>.)
135     *
136     * <P>However, most of this is done by parsing a class file or generating a class file into BCEL's internal data structure.
137     * <B>Therefore, all that is really done here is look up the class file from BCEL's repository.</B>
138     * This is also motivated by the fact that some omitted things
139     * (like the check for extra bytes at the end of the class file) are handy when actually using BCEL to repair a class file
140     * (otherwise you would not be able to load it into BCEL).</P>
141     *
142     * @see org.apache.bcel.Repository
143     * @see org.apache.bcel.Const#JVM_CLASSFILE_MAGIC
144     */
145    @Override
146    public VerificationResult do_verify() {
147        JavaClass jc;
148        try{
149            jc = getJavaClass();    //loads in the class file if not already done.
150
151            if (jc != null) {
152                /* If we find more constraints to check, we should do this in an own method. */
153                if (! myOwner.getClassName().equals(jc.getClassName())) {
154                    // This should maybe caught by BCEL: In case of renamed .class files we get wrong
155                    // JavaClass objects here.
156                    throw new LoadingException("Wrong name: the internal name of the .class file '"+jc.getClassName()+
157                        "' does not match the file's name '"+myOwner.getClassName()+"'.");
158                }
159            }
160
161        }
162        catch(final LoadingException e) {
163            return new VerificationResult(VerificationResult.VERIFIED_REJECTED, e.getMessage());
164        }
165        catch(final ClassFormatException e) {
166            return new VerificationResult(VerificationResult.VERIFIED_REJECTED, e.getMessage());
167        }
168        catch(final RuntimeException e) {
169            // BCEL does not catch every possible RuntimeException; e.g. if
170            // a constant pool index is referenced that does not exist.
171            return new VerificationResult(VerificationResult.VERIFIED_REJECTED, "Parsing via BCEL did not succeed. "+
172                e.getClass().getName()+" occured:\n"+Utility.getStackTrace(e));
173        }
174
175        if (jc != null) {
176            return VerificationResult.VR_OK;
177        }
178        //TODO: Maybe change Repository's behavior to throw a LoadingException instead of just returning "null"
179        //      if a class file cannot be found or in another way be looked up.
180        return new VerificationResult(VerificationResult.VERIFIED_REJECTED, "Repository.lookup() failed. FILE NOT FOUND?");
181    }
182
183    /**
184     * Currently this returns an empty array of String.
185     * One could parse the error messages of BCEL
186     * (written to java.lang.System.err) when loading
187     * a class file such as detecting unknown attributes
188     * or trailing garbage at the end of a class file.
189     * However, Markus Dahm does not like the idea so this
190     * method is currently useless and therefore marked as
191     * <B>TODO</B>.
192     */
193    @Override
194    public String[] getMessages() {
195        // This method is only here to override the javadoc-comment.
196        return super.getMessages();
197    }
198
199}