    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}