    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 */
    017package org.apache.bcel.verifier.structurals;
    018
    019import java.util.ArrayList;
    020import java.util.HashMap;
    021import java.util.HashSet;
    022import java.util.List;
    023import java.util.Map;
    024import java.util.Set;
    025
    026import org.apache.bcel.generic.ASTORE;
    027import org.apache.bcel.generic.ATHROW;
    028import org.apache.bcel.generic.BranchInstruction;
    029import org.apache.bcel.generic.CodeExceptionGen;
    030import org.apache.bcel.generic.GotoInstruction;
    031import org.apache.bcel.generic.IndexedInstruction;
    032import org.apache.bcel.generic.Instruction;
    033import org.apache.bcel.generic.InstructionHandle;
    034import org.apache.bcel.generic.JsrInstruction;
    035import org.apache.bcel.generic.LocalVariableInstruction;
    036import org.apache.bcel.generic.MethodGen;
    037import org.apache.bcel.generic.RET;
    038import org.apache.bcel.generic.ReturnInstruction;
    039import org.apache.bcel.generic.Select;
    040import org.apache.bcel.verifier.exc.AssertionViolatedException;
    041import org.apache.bcel.verifier.exc.StructuralCodeConstraintException;
    042
    043/**
    044 * Instances of this class contain information about the subroutines found in a code array of a method. This
    045 * implementation considers the top-level (the instructions reachable without a JSR or JSR_W starting off from the first
    046 * instruction in a code array of a method) being a special subroutine; see getTopLevel() for that. Please note that the
    047 * definition of subroutines in the Java Virtual Machine Specification, Second Edition is somewhat incomplete.
    048 * Therefore, JustIce uses an own, more rigid notion. Basically, a subroutine is a piece of code that starts at the
    049 * target of a JSR of JSR_W instruction and ends at a corresponding RET instruction. Note also that the control flow of
    050 * a subroutine may be complex and non-linear; and that subroutines may be nested. JustIce also mandates subroutines not
    051 * to be protected by exception handling code (for the sake of control flow predictability). To understand JustIce's
    052 * notion of subroutines, please read
    053 *
    054 * TODO: refer to the paper.
    055 *
    056 * @see #getTopLevel()
    057 */
    058public class Subroutines {
    059    // Node coloring constants
    060    private enum ColourConstants {
    061        WHITE, GRAY, BLACK
    062    }
    063
    064    /**
    065     * This inner class implements the Subroutine interface.
    066     */
    067    private class SubroutineImpl implements Subroutine {
    068        /**
    069         * UNSET, a symbol for an uninitialized localVariable field. This is used for the "top-level" Subroutine; i.e. no
    070         * subroutine.
    071         */
    072        private static final int UNSET = -1;
    073
    074        private final SubroutineImpl[] EMPTY_ARRAY = {};
    075
    076        /**
    077         * The Local Variable slot where the first instruction of this subroutine (an ASTORE) stores the JsrInstruction's
    078         * ReturnAddress in and the RET of this subroutine operates on.
    079         */
    080        private int localVariable = UNSET;
    081
    082        /** The instructions that belong to this subroutine. */
    083        private final Set<InstructionHandle> instructions = new HashSet<>(); // Elements: InstructionHandle
    084
    085        /**
    086         * The JSR or JSR_W instructions that define this subroutine by targeting it.
    087         */
    088        private final Set<InstructionHandle> theJSRs = new HashSet<>();
    089
    090        /**
    091         * The RET instruction that leaves this subroutine.
    092         */
    093        private InstructionHandle theRET;
    094
    095        /**
    096         * The default constructor.
    097         */
    098        public SubroutineImpl() {
    099        }
    100
    101        /**
    102         * A recursive helper method for getRecursivelyAccessedLocalsIndices().
    103         *
    104         * @see #getRecursivelyAccessedLocalsIndices()
    105         */
    106        private void _getRecursivelyAccessedLocalsIndicesHelper(final Set<Integer> set, final Subroutine[] subs) {
    107            for (final Subroutine sub : subs) {
    108                final int[] lvs = sub.getAccessedLocalsIndices();
    109                for (final int lv : lvs) {
    110                    set.add(Integer.valueOf(lv));
    111                }
    112                if (sub.subSubs().length != 0) {
    113                    _getRecursivelyAccessedLocalsIndicesHelper(set, sub.subSubs());
    114                }
    115            }
    116        }
    117
    118        /**
    119         * Adds a new JSR or JSR_W that has this subroutine as its target.
    120         */
    121        public void addEnteringJsrInstruction(final InstructionHandle jsrInst) {
    122            if (jsrInst == null || !(jsrInst.getInstruction() instanceof JsrInstruction)) {
    123                throw new AssertionViolatedException("Expecting JsrInstruction InstructionHandle.");
    124            }
    125            if (localVariable == UNSET) {
    126                throw new AssertionViolatedException("Set the localVariable first!");
    127            }
    128            // Something is wrong when an ASTORE is targeted that does not operate on the same local variable than the rest of the
    129            // JsrInstruction-targets and the RET.
    130            // (We don't know out leader here so we cannot check if we're really targeted!)
    131            if (localVariable != ((ASTORE) ((JsrInstruction) jsrInst.getInstruction()).getTarget().getInstruction()).getIndex()) {
    132                throw new AssertionViolatedException("Setting a wrong JsrInstruction.");
    133            }
    134            theJSRs.add(jsrInst);
    135        }
    136
    137        /*
    138         * Adds an instruction to this subroutine. All instructions must have been added before invoking setLeavingRET().
    139         *
    140         * @see #setLeavingRET
    141         */
    142        void addInstruction(final InstructionHandle ih) {
    143            if (theRET != null) {
    144                throw new AssertionViolatedException("All instructions must have been added before invoking setLeavingRET().");
    145            }
    146            instructions.add(ih);
    147        }
    148
    149        /*
    150         * Refer to the Subroutine interface for documentation.
    151         */
    152        @Override
    153        public boolean contains(final InstructionHandle inst) {
    154            return instructions.contains(inst);
    155        }
    156
    157        /*
    158         * Satisfies Subroutine.getAccessedLocalIndices().
    159         */
    160        @Override
    161        public int[] getAccessedLocalsIndices() {
    162            // TODO: Implement caching.
    163            final Set<Integer> acc = new HashSet<>();
    164            if (theRET == null && this != getTopLevel()) {
    165                throw new AssertionViolatedException("This subroutine object must be built up completely before calculating accessed locals.");
    166            }
    167            {
    168                for (final InstructionHandle ih : instructions) {
    169                    // RET is not a LocalVariableInstruction in the current version of BCEL.
    170                    if (ih.getInstruction() instanceof LocalVariableInstruction || ih.getInstruction() instanceof RET) {
    171                        final int idx = ((IndexedInstruction) ih.getInstruction()).getIndex();
    172                        acc.add(Integer.valueOf(idx));
    173                        // LONG? DOUBLE?.
    174                        try {
    175                            // LocalVariableInstruction instances are typed without the need to look into
    176                            // the constant pool.
    177                            if (ih.getInstruction() instanceof LocalVariableInstruction) {
    178                                final int s = ((LocalVariableInstruction) ih.getInstruction()).getType(null).getSize();
    179                                if (s == 2) {
    180                                    acc.add(Integer.valueOf(idx + 1));
    181                                }
    182                            }
    183                        } catch (final RuntimeException re) {
    184                            throw new AssertionViolatedException("BCEL did not like NULL as a ConstantPoolGen object.", re);
    185                        }
    186                    }
    187                }
    188            }
    189
    190            {
    191                final int[] ret = new int[acc.size()];
    192                int j = -1;
    193                for (final Integer accessedLocal : acc) {
    194                    j++;
    195                    ret[j] = accessedLocal.intValue();
    196                }
    197                return ret;
    198            }
    199        }
    200
    201        /*
    202         * Refer to the Subroutine interface for documentation.
    203         */
    204        @Override
    205        public InstructionHandle[] getEnteringJsrInstructions() {
    206            if (this == getTopLevel()) {
    207                throw new AssertionViolatedException("getLeavingRET() called on top level pseudo-subroutine.");
    208            }
    209            return theJSRs.toArray(InstructionHandle.EMPTY_ARRAY);
    210        }
    211
    212        /*
    213         * Refer to the Subroutine interface for documentation.
    214         */
    215        @Override
    216        public InstructionHandle[] getInstructions() {
    217            return instructions.toArray(InstructionHandle.EMPTY_ARRAY);
    218        }
    219
    220        /*
    221         * Refer to the Subroutine interface for documentation.
    222         */
    223        @Override
    224        public InstructionHandle getLeavingRET() {
    225            if (this == getTopLevel()) {
    226                throw new AssertionViolatedException("getLeavingRET() called on top level pseudo-subroutine.");
    227            }
    228            return theRET;
    229        }
    230
    231        /* Satisfies Subroutine.getRecursivelyAccessedLocalsIndices(). */
    232        @Override
    233        public int[] getRecursivelyAccessedLocalsIndices() {
    234            final Set<Integer> s = new HashSet<>();
    235            final int[] lvs = getAccessedLocalsIndices();
    236            for (final int lv : lvs) {
    237                s.add(Integer.valueOf(lv));
    238            }
    239            _getRecursivelyAccessedLocalsIndicesHelper(s, this.subSubs());
    240            final int[] ret = new int[s.size()];
    241            int j = -1;
    242            for (final Integer index : s) {
    243                j++;
    244                ret[j] = index.intValue();
    245            }
    246            return ret;
    247        }
    248
    249        /**
    250         * Sets the leaving RET instruction. Must be invoked after all instructions are added. Must not be invoked for top-level
    251         * 'subroutine'.
    252         */
    253        void setLeavingRET() {
    254            if (localVariable == UNSET) {
    255                throw new AssertionViolatedException("setLeavingRET() called for top-level 'subroutine' or forgot to set local variable first.");
    256            }
    257            InstructionHandle ret = null;
    258            for (final InstructionHandle actual : instructions) {
    259                if (actual.getInstruction() instanceof RET) {
    260                    if (ret != null) {
    261                        throw new StructuralCodeConstraintException("Subroutine with more then one RET detected: '" + ret + "' and '" + actual + "'.");
    262                    }
    263                    ret = actual;
    264                }
    265            }
    266            if (ret == null) {
    267                throw new StructuralCodeConstraintException("Subroutine without a RET detected.");
    268            }
    269            if (((RET) ret.getInstruction()).getIndex() != localVariable) {
    270                throw new StructuralCodeConstraintException(
    271                    "Subroutine uses '" + ret + "' which does not match the correct local variable '" + localVariable + "'.");
    272            }
    273            theRET = ret;
    274        }
    275
    276        /*
    277         * Sets the local variable slot the ASTORE that is targeted by the JsrInstructions of this subroutine operates on. This
    278         * subroutine's RET operates on that same local variable slot, of course.
    279         */
    280        void setLocalVariable(final int i) {
    281            if (localVariable != UNSET) {
    282                throw new AssertionViolatedException("localVariable set twice.");
    283            }
    284            localVariable = i;
    285        }
    286
    287        /*
    288         * Satisfies Subroutine.subSubs().
    289         */
    290        @Override
    291        public Subroutine[] subSubs() {
    292            final Set<Subroutine> h = new HashSet<>();
    293
    294            for (final InstructionHandle ih : instructions) {
    295                final Instruction inst = ih.getInstruction();
    296                if (inst instanceof JsrInstruction) {
    297                    final InstructionHandle targ = ((JsrInstruction) inst).getTarget();
    298                    h.add(getSubroutine(targ));
    299                }
    300            }
    301            return h.toArray(EMPTY_ARRAY);
    302        }
    303
    304        /**
    305         * Returns a String representation of this object, merely for debugging purposes. (Internal) Warning: Verbosity on a
    306         * problematic subroutine may cause stack overflow errors due to recursive subSubs() calls. Don't use this, then.
    307         */
    308        @Override
    309        public String toString() {
    310            final StringBuilder ret = new StringBuilder();
    311            ret.append("Subroutine: Local variable is '").append(localVariable);
    312            ret.append("', JSRs are '").append(theJSRs);
    313            ret.append("', RET is '").append(theRET);
    314            ret.append("', Instructions: '").append(instructions).append("'.");
    315
    316            ret.append(" Accessed local variable slots: '");
    317            int[] alv = getAccessedLocalsIndices();
    318            for (final int element : alv) {
    319                ret.append(element);
    320                ret.append(" ");
    321            }
    322            ret.append("'.");
    323
    324            ret.append(" Recursively (via subsub...routines) accessed local variable slots: '");
    325            alv = getRecursivelyAccessedLocalsIndices();
    326            for (final int element : alv) {
    327                ret.append(element);
    328                ret.append(" ");
    329            }
    330            ret.append("'.");
    331
    332            return ret.toString();
    333        }
    334
    335    }// end Inner Class SubrouteImpl
    336
    337    /**
    338     * A utility method that calculates the successors of a given InstructionHandle <B>in the same subroutine</B>. That
    339     * means, a RET does not have any successors as defined here. A JsrInstruction has its physical successor as its
    340     * successor (opposed to its target) as defined here.
    341     */
    342    private static InstructionHandle[] getSuccessors(final InstructionHandle instruction) {
    343        final InstructionHandle[] single = new InstructionHandle[1];
    344
    345        final Instruction inst = instruction.getInstruction();
    346
    347        // Terminates method normally.
    348        // Terminates method abnormally, because JustIce mandates
    349        // subroutines not to be protected by exception handlers.
    350        if (inst instanceof RET || inst instanceof ReturnInstruction || inst instanceof ATHROW) {
    351            return InstructionHandle.EMPTY_ARRAY;
    352        }
    353
    354        // See method comment.
    355        if (inst instanceof JsrInstruction) {
    356            single[0] = instruction.getNext();
    357            return single;
    358        }
    359
    360        if (inst instanceof GotoInstruction) {
    361            single[0] = ((GotoInstruction) inst).getTarget();
    362            return single;
    363        }
    364
    365        if (inst instanceof BranchInstruction) {
    366            if (inst instanceof Select) {
    367                // BCEL's getTargets() returns only the non-default targets,
    368                // thanks to Eli Tilevich for reporting.
    369                final InstructionHandle[] matchTargets = ((Select) inst).getTargets();
    370                final InstructionHandle[] ret = new InstructionHandle[matchTargets.length + 1];
    371                ret[0] = ((Select) inst).getTarget();
    372                System.arraycopy(matchTargets, 0, ret, 1, matchTargets.length);
    373                return ret;
    374            }
    375            final InstructionHandle[] pair = new InstructionHandle[2];
    376            pair[0] = instruction.getNext();
    377            pair[1] = ((BranchInstruction) inst).getTarget();
    378            return pair;
    379        }
    380
    381        // default case: Fall through.
    382        single[0] = instruction.getNext();
    383        return single;
    384    }
    385
    386    /**
    387     * The map containing the subroutines found. Key: InstructionHandle of the leader of the subroutine. Elements:
    388     * SubroutineImpl objects.
    389     */
    390    private final Map<InstructionHandle, Subroutine> subroutines = new HashMap<>();
    391
    392    /**
    393     * This is referring to a special subroutine, namely the top level. This is not really a subroutine but we use it to
    394     * distinguish between top level instructions and unreachable instructions.
    395     */
    396    // CHECKSTYLE:OFF
    397    public final Subroutine TOPLEVEL; // TODO can this be made private?
    398    // CHECKSTYLE:ON
    399
    400    /**
    401     * Constructor.
    402     *
    403     * @param mg A MethodGen object representing method to create the Subroutine objects of. Assumes that JustIce strict
    404     *        checks are needed.
    405     */
    406    public Subroutines(final MethodGen mg) {
    407        this(mg, true);
    408    }
    409
    410    /**
    411     * Constructor.
    412     *
    413     * @param mg A MethodGen object representing method to create the Subroutine objects of.
    414     * @param enableJustIceCheck whether to enable additional JustIce checks
    415     * @since 6.0
    416     */
    417    public Subroutines(final MethodGen mg, final boolean enableJustIceCheck) {
    418        final InstructionHandle[] all = mg.getInstructionList().getInstructionHandles();
    419        final CodeExceptionGen[] handlers = mg.getExceptionHandlers();
    420
    421        // Define our "Toplevel" fake subroutine.
    422        TOPLEVEL = new SubroutineImpl();
    423
    424        // Calculate "real" subroutines.
    425        final Set<InstructionHandle> subLeaders = new HashSet<>(); // Elements: InstructionHandle
    426        for (final InstructionHandle element : all) {
    427            final Instruction inst = element.getInstruction();
    428            if (inst instanceof JsrInstruction) {
    429                subLeaders.add(((JsrInstruction) inst).getTarget());
    430            }
    431        }
    432
    433        // Build up the database.
    434        for (final InstructionHandle astore : subLeaders) {
    435            final SubroutineImpl sr = new SubroutineImpl();
    436            sr.setLocalVariable(((ASTORE) astore.getInstruction()).getIndex());
    437            subroutines.put(astore, sr);
    438        }
    439
    440        // Fake it a bit. We want a virtual "TopLevel" subroutine.
    441        subroutines.put(all[0], TOPLEVEL);
    442        subLeaders.add(all[0]);
    443
    444        // Tell the subroutines about their JsrInstructions.
    445        // Note that there cannot be a JSR targeting the top-level
    446        // since "Jsr 0" is disallowed in Pass 3a.
    447        // Instructions shared by a subroutine and the toplevel are
    448        // disallowed and checked below, after the BFS.
    449        for (final InstructionHandle element : all) {
    450            final Instruction inst = element.getInstruction();
    451            if (inst instanceof JsrInstruction) {
    452                final InstructionHandle leader = ((JsrInstruction) inst).getTarget();
    453                ((SubroutineImpl) getSubroutine(leader)).addEnteringJsrInstruction(element);
    454            }
    455        }
    456
    457        // Now do a BFS from every subroutine leader to find all the
    458        // instructions that belong to a subroutine.
    459        // we don't want to assign an instruction to two or more Subroutine objects.
    460        final Set<InstructionHandle> instructionsAssigned = new HashSet<>();
    461
    462        // Graph coloring. Key: InstructionHandle, Value: ColourConstants enum .
    463        final Map<InstructionHandle, ColourConstants> colors = new HashMap<>();
    464
    465        final List<InstructionHandle> qList = new ArrayList<>();
    466        for (final InstructionHandle actual : subLeaders) {
    467            // Do some BFS with "actual" as the root of the graph.
    468            // Init colors
    469            for (final InstructionHandle element : all) {
    470                colors.put(element, ColourConstants.WHITE);
    471            }
    472            colors.put(actual, ColourConstants.GRAY);
    473            // Init Queue
    474
    475            qList.clear();
    476            qList.add(actual); // add(Obj) adds to the end, remove(0) removes from the start.
    477
    478            /*
    479             * BFS ALGORITHM MODIFICATION: Start out with multiple "root" nodes, as exception handlers are starting points of
    480             * top-level code, too. [why top-level? TODO: Refer to the special JustIce notion of subroutines.]
    481             */
    482            if (actual == all[0]) {
    483                for (final CodeExceptionGen handler : handlers) {
    484                    colors.put(handler.getHandlerPC(), ColourConstants.GRAY);
    485                    qList.add(handler.getHandlerPC());
    486                }
    487            }
    488            /* CONTINUE NORMAL BFS ALGORITHM */
    489
    490            // Loop until Queue is empty
    491            while (!qList.isEmpty()) {
    492                final InstructionHandle u = qList.remove(0);
    493                final InstructionHandle[] successors = getSuccessors(u);
    494                for (final InstructionHandle successor : successors) {
    495                    if (colors.get(successor) == ColourConstants.WHITE) {
    496                        colors.put(successor, ColourConstants.GRAY);
    497                        qList.add(successor);
    498                    }
    499                }
    500                colors.put(u, ColourConstants.BLACK);
    501            }
    502            // BFS ended above.
    503            for (final InstructionHandle element : all) {
    504                if (colors.get(element) == ColourConstants.BLACK) {
    505                    ((SubroutineImpl) (actual == all[0] ? getTopLevel() : getSubroutine(actual))).addInstruction(element);
    506                    if (instructionsAssigned.contains(element)) {
    507                        throw new StructuralCodeConstraintException(
    508                            "Instruction '" + element + "' is part of more than one subroutine (or of the top level and a subroutine).");
    509                    }
    510                    instructionsAssigned.add(element);
    511                }
    512            }
    513            if (actual != all[0]) {// If we don't deal with the top-level 'subroutine'
    514                ((SubroutineImpl) getSubroutine(actual)).setLeavingRET();
    515            }
    516        }
    517
    518        if (enableJustIceCheck) {
    519            // Now make sure no instruction of a Subroutine is protected by exception handling code
    520            // as is mandated by JustIces notion of subroutines.
    521            for (final CodeExceptionGen handler : handlers) {
    522                InstructionHandle _protected = handler.getStartPC();
    523                while (_protected != handler.getEndPC().getNext()) {
    524                    // Note the inclusive/inclusive notation of "generic API" exception handlers!
    525                    for (final Subroutine sub : subroutines.values()) {
    526                        if (sub != subroutines.get(all[0]) && sub.contains(_protected)) {
    527                            throw new StructuralCodeConstraintException("Subroutine instruction '" + _protected + "' is protected by an exception handler, '"
    528                                + handler + "'. This is forbidden by the JustIce verifier due to its clear definition of subroutines.");
    529                        }
    530                    }
    531                    _protected = _protected.getNext();
    532                }
    533            }
    534        }
    535
    536        // Now make sure no subroutine is calling a subroutine
    537        // that uses the same local variable for the RET as themselves
    538        // (recursively).
    539        // This includes that subroutines may not call themselves
    540        // recursively, even not through intermediate calls to other
    541        // subroutines.
    542        noRecursiveCalls(getTopLevel(), new HashSet<>());
    543
    544    }
    545
    546    /**
    547     * Returns the Subroutine object associated with the given leader (that is, the first instruction of the subroutine).
    548     * You must not use this to get the top-level instructions modeled as a Subroutine object.
    549     *
    550     * @see #getTopLevel()
    551     */
    552    public Subroutine getSubroutine(final InstructionHandle leader) {
    553        final Subroutine ret = subroutines.get(leader);
    554
    555        if (ret == null) {
    556            throw new AssertionViolatedException("Subroutine requested for an InstructionHandle that is not a leader of a subroutine.");
    557        }
    558
    559        if (ret == TOPLEVEL) {
    560            throw new AssertionViolatedException("TOPLEVEL special subroutine requested; use getTopLevel().");
    561        }
    562
    563        return ret;
    564    }
    565
    566    /**
    567     * For easy handling, the piece of code that is <B>not</B> a subroutine, the top-level, is also modeled as a Subroutine
    568     * object. It is a special Subroutine object where <B>you must not invoke getEnteringJsrInstructions() or
    569     * getLeavingRET()</B>.
    570     *
    571     * @see Subroutine#getEnteringJsrInstructions()
    572     * @see Subroutine#getLeavingRET()
    573     */
    574    public Subroutine getTopLevel() {
    575        return TOPLEVEL;
    576    }
    577
    578    /**
    579     * This (recursive) utility method makes sure that no subroutine is calling a subroutine that uses the same local
    580     * variable for the RET as themselves (recursively). This includes that subroutines may not call themselves recursively,
    581     * even not through intermediate calls to other subroutines.
    582     *
    583     * @throws StructuralCodeConstraintException if the above constraint is not satisfied.
    584     */
    585    private void noRecursiveCalls(final Subroutine sub, final Set<Integer> set) {
    586        final Subroutine[] subs = sub.subSubs();
    587
    588        for (final Subroutine sub2 : subs) {
    589            final int index = ((RET) sub2.getLeavingRET().getInstruction()).getIndex();
    590
    591            if (!set.add(Integer.valueOf(index))) {
    592                // Don't use toString() here because of possibly infinite recursive subSubs() calls then.
    593                final SubroutineImpl si = (SubroutineImpl) sub2;
    594                throw new StructuralCodeConstraintException("Subroutine with local variable '" + si.localVariable + "', JSRs '" + si.theJSRs + "', RET '"
    595                    + si.theRET + "' is called by a subroutine which uses the same local variable index as itself; maybe even a recursive call?"
    596                    + " JustIce's clean definition of a subroutine forbids both.");
    597            }
    598
    599            noRecursiveCalls(sub2, set);
    600
    601            set.remove(Integer.valueOf(index));
    602        }
    603    }
    604
    605    /**
    606     * Returns the subroutine object associated with the given instruction. This is a costly operation, you should consider
    607     * using getSubroutine(InstructionHandle). Returns 'null' if the given InstructionHandle lies in so-called 'dead code',
    608     * i.e. code that can never be executed.
    609     *
    610     * @see #getSubroutine(InstructionHandle)
    611     * @see #getTopLevel()
    612     */
    613    public Subroutine subroutineOf(final InstructionHandle any) {
    614        for (final Subroutine s : subroutines.values()) {
    615            if (s.contains(any)) {
    616                return s;
    617            }
    618        }
    619        System.err.println("DEBUG: Please verify '" + any.toString(true) + "' lies in dead code.");
    620        return null;
    621        // throw new AssertionViolatedException("No subroutine for InstructionHandle found (DEAD CODE?).");
    622    }
    623
    624    /**
    625     * Returns a String representation of this object; merely for debugging puposes.
    626     */
    627    @Override
    628    public String toString() {
    629        return "---\n" + subroutines + "\n---\n";
    630    }
    631}