    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one
    003 * or more contributor license agreements.  See the NOTICE file
    004 * distributed with this work for additional information
    005 * regarding copyright ownership.  The ASF licenses this file
    006 * to you under the Apache License, Version 2.0 (the
    007 * "License"); you may not use this file except in compliance
    008 * with the License.  You may obtain a copy of the License at
    009 *
    010 *   https://www.apache.org/licenses/LICENSE-2.0
    011 *
    012 * Unless required by applicable law or agreed to in writing,
    013 * software distributed under the License is distributed on an
    014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
    015 * KIND, either express or implied.  See the License for the
    016 * specific language governing permissions and limitations
    017 * under the License.
    018 */
    019package org.apache.bcel.verifier.structurals;
    020
    021import java.util.ArrayList;
    022import java.util.HashMap;
    023import java.util.HashSet;
    024import java.util.List;
    025import java.util.Map;
    026import java.util.Set;
    027
    028import org.apache.bcel.generic.ASTORE;
    029import org.apache.bcel.generic.ATHROW;
    030import org.apache.bcel.generic.BranchInstruction;
    031import org.apache.bcel.generic.CodeExceptionGen;
    032import org.apache.bcel.generic.GotoInstruction;
    033import org.apache.bcel.generic.IndexedInstruction;
    034import org.apache.bcel.generic.Instruction;
    035import org.apache.bcel.generic.InstructionHandle;
    036import org.apache.bcel.generic.JsrInstruction;
    037import org.apache.bcel.generic.LocalVariableInstruction;
    038import org.apache.bcel.generic.MethodGen;
    039import org.apache.bcel.generic.RET;
    040import org.apache.bcel.generic.ReturnInstruction;
    041import org.apache.bcel.generic.Select;
    042import org.apache.bcel.verifier.exc.AssertionViolatedException;
    043import org.apache.bcel.verifier.exc.StructuralCodeConstraintException;
    044
    045/**
    046 * Instances of this class contain information about the subroutines found in a code array of a method. This
    047 * implementation considers the top-level (the instructions reachable without a JSR or JSR_W starting off from the first
    048 * instruction in a code array of a method) being a special subroutine; see getTopLevel() for that. Please note that the
    049 * definition of subroutines in the Java Virtual Machine Specification, Second Edition is somewhat incomplete.
    050 * Therefore, JustIce uses an own, more rigid notion. Basically, a subroutine is a piece of code that starts at the
    051 * target of a JSR of JSR_W instruction and ends at a corresponding RET instruction. Note also that the control flow of
    052 * a subroutine may be complex and non-linear; and that subroutines may be nested. JustIce also mandates subroutines not
    053 * to be protected by exception handling code (for the sake of control flow predictability). To understand JustIce's
    054 * notion of subroutines, please read
    055 *
    056 * TODO: refer to the paper.
    057 *
    058 * @see #getTopLevel()
    059 */
    060public class Subroutines {
    061    // Node coloring constants
    062    private enum ColourConstants {
    063        WHITE, GRAY, BLACK
    064    }
    065
    066    /**
    067     * This inner class implements the Subroutine interface.
    068     */
    069    private final class SubroutineImpl implements Subroutine {
    070        /**
    071         * UNSET, a symbol for an uninitialized localVariable field. This is used for the "top-level" Subroutine; i.e. no
    072         * subroutine.
    073         */
    074        private static final int UNSET = -1;
    075
    076        private final SubroutineImpl[] EMPTY_ARRAY = {};
    077
    078        /**
    079         * The Local Variable slot where the first instruction of this subroutine (an ASTORE) stores the JsrInstruction's
    080         * ReturnAddress in and the RET of this subroutine operates on.
    081         */
    082        private int localVariable = UNSET;
    083
    084        /** The instructions that belong to this subroutine. */
    085        private final Set<InstructionHandle> instructions = new HashSet<>(); // Elements: InstructionHandle
    086
    087        /**
    088         * The JSR or JSR_W instructions that define this subroutine by targeting it.
    089         */
    090        private final Set<InstructionHandle> theJSRs = new HashSet<>();
    091
    092        /**
    093         * The RET instruction that leaves this subroutine.
    094         */
    095        private InstructionHandle theRET;
    096
    097        /**
    098         * Constructs a new instance.
    099         */
    100        SubroutineImpl() {
    101            // empty
    102        }
    103
    104        /**
    105         * Adds a new JSR or JSR_W that has this subroutine as its target.
    106         */
    107        public void addEnteringJsrInstruction(final InstructionHandle jsrInst) {
    108            if (jsrInst == null || !(jsrInst.getInstruction() instanceof JsrInstruction)) {
    109                throw new AssertionViolatedException("Expecting JsrInstruction InstructionHandle.");
    110            }
    111            if (localVariable == UNSET) {
    112                throw new AssertionViolatedException("Set the localVariable first!");
    113            }
    114            // Something is wrong when an ASTORE is targeted that does not operate on the same local variable than the rest of the
    115            // JsrInstruction-targets and the RET.
    116            // (We don't know out leader here so we cannot check if we're really targeted!)
    117            if (localVariable != ((ASTORE) ((JsrInstruction) jsrInst.getInstruction()).getTarget().getInstruction()).getIndex()) {
    118                throw new AssertionViolatedException("Setting a wrong JsrInstruction.");
    119            }
    120            theJSRs.add(jsrInst);
    121        }
    122
    123        /*
    124         * Adds an instruction to this subroutine. All instructions must have been added before invoking setLeavingRET().
    125         *
    126         * @see #setLeavingRET
    127         */
    128        void addInstruction(final InstructionHandle ih) {
    129            if (theRET != null) {
    130                throw new AssertionViolatedException("All instructions must have been added before invoking setLeavingRET().");
    131            }
    132            instructions.add(ih);
    133        }
    134
    135        /*
    136         * Refer to the Subroutine interface for documentation.
    137         */
    138        @Override
    139        public boolean contains(final InstructionHandle inst) {
    140            return instructions.contains(inst);
    141        }
    142
    143        /*
    144         * Satisfies Subroutine.getAccessedLocalIndices().
    145         */
    146        @Override
    147        public int[] getAccessedLocalsIndices() {
    148            // TODO: Implement caching.
    149            final Set<Integer> acc = new HashSet<>();
    150            if (theRET == null && this != getTopLevel()) {
    151                throw new AssertionViolatedException("This subroutine object must be built up completely before calculating accessed locals.");
    152            }
    153            {
    154                for (final InstructionHandle ih : instructions) {
    155                    // RET is not a LocalVariableInstruction in the current version of BCEL.
    156                    if (ih.getInstruction() instanceof LocalVariableInstruction || ih.getInstruction() instanceof RET) {
    157                        final int idx = ((IndexedInstruction) ih.getInstruction()).getIndex();
    158                        acc.add(Integer.valueOf(idx));
    159                        // LONG? DOUBLE?.
    160                        try {
    161                            // LocalVariableInstruction instances are typed without the need to look into
    162                            // the constant pool.
    163                            if (ih.getInstruction() instanceof LocalVariableInstruction) {
    164                                final int s = ((LocalVariableInstruction) ih.getInstruction()).getType(null).getSize();
    165                                if (s == 2) {
    166                                    acc.add(Integer.valueOf(idx + 1));
    167                                }
    168                            }
    169                        } catch (final RuntimeException re) {
    170                            throw new AssertionViolatedException("BCEL did not like NULL as a ConstantPoolGen object.", re);
    171                        }
    172                    }
    173                }
    174            }
    175
    176            {
    177                final int[] ret = new int[acc.size()];
    178                int j = -1;
    179                for (final Integer accessedLocal : acc) {
    180                    j++;
    181                    ret[j] = accessedLocal.intValue();
    182                }
    183                return ret;
    184            }
    185        }
    186
    187        /*
    188         * Refer to the Subroutine interface for documentation.
    189         */
    190        @Override
    191        public InstructionHandle[] getEnteringJsrInstructions() {
    192            if (this == getTopLevel()) {
    193                throw new AssertionViolatedException("getLeavingRET() called on top level pseudo-subroutine.");
    194            }
    195            return theJSRs.toArray(InstructionHandle.EMPTY_ARRAY);
    196        }
    197
    198        /*
    199         * Refer to the Subroutine interface for documentation.
    200         */
    201        @Override
    202        public InstructionHandle[] getInstructions() {
    203            return instructions.toArray(InstructionHandle.EMPTY_ARRAY);
    204        }
    205
    206        /*
    207         * Refer to the Subroutine interface for documentation.
    208         */
    209        @Override
    210        public InstructionHandle getLeavingRET() {
    211            if (this == getTopLevel()) {
    212                throw new AssertionViolatedException("getLeavingRET() called on top level pseudo-subroutine.");
    213            }
    214            return theRET;
    215        }
    216
    217        /* Satisfies Subroutine.getRecursivelyAccessedLocalsIndices(). */
    218        @Override
    219        public int[] getRecursivelyAccessedLocalsIndices() {
    220            final Set<Integer> s = new HashSet<>();
    221            final int[] lvs = getAccessedLocalsIndices();
    222            for (final int lv : lvs) {
    223                s.add(Integer.valueOf(lv));
    224            }
    225            getRecursivelyAccessedLocalsIndicesHelper(s, subSubs());
    226            final int[] ret = new int[s.size()];
    227            int j = -1;
    228            for (final Integer index : s) {
    229                j++;
    230                ret[j] = index.intValue();
    231            }
    232            return ret;
    233        }
    234
    235        /**
    236         * A recursive helper method for getRecursivelyAccessedLocalsIndices().
    237         *
    238         * @see #getRecursivelyAccessedLocalsIndices()
    239         */
    240        private void getRecursivelyAccessedLocalsIndicesHelper(final Set<Integer> set, final Subroutine[] subs) {
    241            for (final Subroutine sub : subs) {
    242                final int[] lvs = sub.getAccessedLocalsIndices();
    243                for (final int lv : lvs) {
    244                    set.add(Integer.valueOf(lv));
    245                }
    246                if (sub.subSubs().length != 0) {
    247                    getRecursivelyAccessedLocalsIndicesHelper(set, sub.subSubs());
    248                }
    249            }
    250        }
    251
    252        /**
    253         * Sets the leaving RET instruction. Must be invoked after all instructions are added. Must not be invoked for top-level
    254         * 'subroutine'.
    255         */
    256        void setLeavingRET() {
    257            if (localVariable == UNSET) {
    258                throw new AssertionViolatedException("setLeavingRET() called for top-level 'subroutine' or forgot to set local variable first.");
    259            }
    260            InstructionHandle ret = null;
    261            for (final InstructionHandle actual : instructions) {
    262                if (actual.getInstruction() instanceof RET) {
    263                    if (ret != null) {
    264                        throw new StructuralCodeConstraintException("Subroutine with more then one RET detected: '" + ret + "' and '" + actual + "'.");
    265                    }
    266                    ret = actual;
    267                }
    268            }
    269            if (ret == null) {
    270                throw new StructuralCodeConstraintException("Subroutine without a RET detected.");
    271            }
    272            if (((RET) ret.getInstruction()).getIndex() != localVariable) {
    273                throw new StructuralCodeConstraintException(
    274                    "Subroutine uses '" + ret + "' which does not match the correct local variable '" + localVariable + "'.");
    275            }
    276            theRET = ret;
    277        }
    278
    279        /*
    280         * Sets the local variable slot the ASTORE that is targeted by the JsrInstructions of this subroutine operates on. This
    281         * subroutine's RET operates on that same local variable slot, of course.
    282         */
    283        void setLocalVariable(final int i) {
    284            if (localVariable != UNSET) {
    285                throw new AssertionViolatedException("localVariable set twice.");
    286            }
    287            localVariable = i;
    288        }
    289
    290        /*
    291         * Satisfies Subroutine.subSubs().
    292         */
    293        @Override
    294        public Subroutine[] subSubs() {
    295            final Set<Subroutine> h = new HashSet<>();
    296
    297            for (final InstructionHandle ih : instructions) {
    298                final Instruction inst = ih.getInstruction();
    299                if (inst instanceof JsrInstruction) {
    300                    final InstructionHandle targ = ((JsrInstruction) inst).getTarget();
    301                    h.add(getSubroutine(targ));
    302                }
    303            }
    304            return h.toArray(EMPTY_ARRAY);
    305        }
    306
    307        /**
    308         * Returns a String representation of this object, merely for debugging purposes. (Internal) Warning: Verbosity on a
    309         * problematic subroutine may cause stack overflow errors due to recursive subSubs() calls. Don't use this, then.
    310         */
    311        @Override
    312        public String toString() {
    313            final StringBuilder ret = new StringBuilder();
    314            ret.append("Subroutine: Local variable is '").append(localVariable);
    315            ret.append("', JSRs are '").append(theJSRs);
    316            ret.append("', RET is '").append(theRET);
    317            ret.append("', Instructions: '").append(instructions).append("'.");
    318
    319            ret.append(" Accessed local variable slots: '");
    320            int[] alv = getAccessedLocalsIndices();
    321            for (final int element : alv) {
    322                ret.append(element);
    323                ret.append(" ");
    324            }
    325            ret.append("'.");
    326
    327            ret.append(" Recursively (via subsub...routines) accessed local variable slots: '");
    328            alv = getRecursivelyAccessedLocalsIndices();
    329            for (final int element : alv) {
    330                ret.append(element);
    331                ret.append(" ");
    332            }
    333            ret.append("'.");
    334
    335            return ret.toString();
    336        }
    337
    338    } // end Inner Class SubrouteImpl
    339
    340    /**
    341     * A utility method that calculates the successors of a given InstructionHandle <B>in the same subroutine</B>. That
    342     * means, a RET does not have any successors as defined here. A JsrInstruction has its physical successor as its
    343     * successor (opposed to its target) as defined here.
    344     */
    345    private static InstructionHandle[] getSuccessors(final InstructionHandle instruction) {
    346        final InstructionHandle[] single = new InstructionHandle[1];
    347
    348        final Instruction inst = instruction.getInstruction();
    349
    350        // Terminates method normally.
    351        // Terminates method abnormally, because JustIce mandates
    352        // subroutines not to be protected by exception handlers.
    353        if (inst instanceof RET || inst instanceof ReturnInstruction || inst instanceof ATHROW) {
    354            return InstructionHandle.EMPTY_ARRAY;
    355        }
    356
    357        // See method comment.
    358        if (inst instanceof JsrInstruction) {
    359            single[0] = instruction.getNext();
    360            return single;
    361        }
    362
    363        if (inst instanceof GotoInstruction) {
    364            single[0] = ((GotoInstruction) inst).getTarget();
    365            return single;
    366        }
    367
    368        if (inst instanceof BranchInstruction) {
    369            if (inst instanceof Select) {
    370                // BCEL's getTargets() returns only the non-default targets,
    371                // thanks to Eli Tilevich for reporting.
    372                final InstructionHandle[] matchTargets = ((Select) inst).getTargets();
    373                final InstructionHandle[] ret = new InstructionHandle[matchTargets.length + 1];
    374                ret[0] = ((Select) inst).getTarget();
    375                System.arraycopy(matchTargets, 0, ret, 1, matchTargets.length);
    376                return ret;
    377            }
    378            final InstructionHandle[] pair = new InstructionHandle[2];
    379            pair[0] = instruction.getNext();
    380            pair[1] = ((BranchInstruction) inst).getTarget();
    381            return pair;
    382        }
    383
    384        // default case: Fall through.
    385        single[0] = instruction.getNext();
    386        return single;
    387    }
    388
    389    /**
    390     * The map containing the subroutines found. Key: InstructionHandle of the leader of the subroutine. Elements:
    391     * SubroutineImpl objects.
    392     */
    393    private final Map<InstructionHandle, Subroutine> subroutines = new HashMap<>();
    394
    395    /**
    396     * This is referring to a special subroutine, namely the top level. This is not really a subroutine but we use it to
    397     * distinguish between top level instructions and unreachable instructions.
    398     */
    399    // CHECKSTYLE:OFF
    400    public final Subroutine TOPLEVEL; // TODO can this be made private?
    401    // CHECKSTYLE:ON
    402
    403    /**
    404     * Constructs a new instance.
    405     *
    406     * @param mg A MethodGen object representing method to create the Subroutine objects of. Assumes that JustIce strict
    407     *        checks are needed.
    408     */
    409    public Subroutines(final MethodGen mg) {
    410        this(mg, true);
    411    }
    412
    413    /**
    414     * Constructs a new instance.
    415     *
    416     * @param mg A MethodGen object representing method to create the Subroutine objects of.
    417     * @param enableJustIceCheck whether to enable additional JustIce checks
    418     * @since 6.0
    419     */
    420    public Subroutines(final MethodGen mg, final boolean enableJustIceCheck) {
    421        final InstructionHandle[] all = mg.getInstructionList().getInstructionHandles();
    422        final CodeExceptionGen[] handlers = mg.getExceptionHandlers();
    423
    424        // Define our "Toplevel" fake subroutine.
    425        TOPLEVEL = new SubroutineImpl();
    426
    427        // Calculate "real" subroutines.
    428        final Set<InstructionHandle> subLeaders = new HashSet<>(); // Elements: InstructionHandle
    429        for (final InstructionHandle element : all) {
    430            final Instruction inst = element.getInstruction();
    431            if (inst instanceof JsrInstruction) {
    432                subLeaders.add(((JsrInstruction) inst).getTarget());
    433            }
    434        }
    435
    436        // Build up the database.
    437        for (final InstructionHandle astore : subLeaders) {
    438            final SubroutineImpl sr = new SubroutineImpl();
    439            sr.setLocalVariable(((ASTORE) astore.getInstruction()).getIndex());
    440            subroutines.put(astore, sr);
    441        }
    442
    443        // Fake it a bit. We want a virtual "TopLevel" subroutine.
    444        subroutines.put(all[0], TOPLEVEL);
    445        subLeaders.add(all[0]);
    446
    447        // Tell the subroutines about their JsrInstructions.
    448        // Note that there cannot be a JSR targeting the top-level
    449        // since "Jsr 0" is disallowed in Pass 3a.
    450        // Instructions shared by a subroutine and the toplevel are
    451        // disallowed and checked below, after the BFS.
    452        for (final InstructionHandle element : all) {
    453            final Instruction inst = element.getInstruction();
    454            if (inst instanceof JsrInstruction) {
    455                final InstructionHandle leader = ((JsrInstruction) inst).getTarget();
    456                ((SubroutineImpl) getSubroutine(leader)).addEnteringJsrInstruction(element);
    457            }
    458        }
    459
    460        // Now do a BFS from every subroutine leader to find all the
    461        // instructions that belong to a subroutine.
    462        // we don't want to assign an instruction to two or more Subroutine objects.
    463        final Set<InstructionHandle> instructionsAssigned = new HashSet<>();
    464
    465        // Graph coloring. Key: InstructionHandle, Value: ColourConstants enum.
    466        final Map<InstructionHandle, ColourConstants> colors = new HashMap<>();
    467
    468        final List<InstructionHandle> qList = new ArrayList<>();
    469        for (final InstructionHandle actual : subLeaders) {
    470            // Do some BFS with "actual" as the root of the graph.
    471            // Init colors
    472            for (final InstructionHandle element : all) {
    473                colors.put(element, ColourConstants.WHITE);
    474            }
    475            colors.put(actual, ColourConstants.GRAY);
    476            // Init Queue
    477
    478            qList.clear();
    479            qList.add(actual); // add(Obj) adds to the end, remove(0) removes from the start.
    480
    481            /*
    482             * BFS ALGORITHM MODIFICATION: Start out with multiple "root" nodes, as exception handlers are starting points of
    483             * top-level code, too. [why top-level? TODO: Refer to the special JustIce notion of subroutines.]
    484             */
    485            if (actual == all[0]) {
    486                for (final CodeExceptionGen handler : handlers) {
    487                    colors.put(handler.getHandlerPC(), ColourConstants.GRAY);
    488                    qList.add(handler.getHandlerPC());
    489                }
    490            }
    491            /* CONTINUE NORMAL BFS ALGORITHM */
    492
    493            // Loop until Queue is empty
    494            while (!qList.isEmpty()) {
    495                final InstructionHandle u = qList.remove(0);
    496                final InstructionHandle[] successors = getSuccessors(u);
    497                for (final InstructionHandle successor : successors) {
    498                    if (colors.get(successor) == ColourConstants.WHITE) {
    499                        colors.put(successor, ColourConstants.GRAY);
    500                        qList.add(successor);
    501                    }
    502                }
    503                colors.put(u, ColourConstants.BLACK);
    504            }
    505            // BFS ended above.
    506            for (final InstructionHandle element : all) {
    507                if (colors.get(element) == ColourConstants.BLACK) {
    508                    ((SubroutineImpl) (actual == all[0] ? getTopLevel() : getSubroutine(actual))).addInstruction(element);
    509                    if (instructionsAssigned.contains(element)) {
    510                        throw new StructuralCodeConstraintException(
    511                            "Instruction '" + element + "' is part of more than one subroutine (or of the top level and a subroutine).");
    512                    }
    513                    instructionsAssigned.add(element);
    514                }
    515            }
    516            if (actual != all[0]) { // If we don't deal with the top-level 'subroutine'
    517                ((SubroutineImpl) getSubroutine(actual)).setLeavingRET();
    518            }
    519        }
    520
    521        if (enableJustIceCheck) {
    522            // Now make sure no instruction of a Subroutine is protected by exception handling code
    523            // as is mandated by JustIces notion of subroutines.
    524            for (final CodeExceptionGen handler : handlers) {
    525                InstructionHandle protectedIh = handler.getStartPC();
    526                while (protectedIh != handler.getEndPC().getNext()) {
    527                    // Note the inclusive/inclusive notation of "generic API" exception handlers!
    528                    for (final Subroutine sub : subroutines.values()) {
    529                        if (sub != subroutines.get(all[0]) && sub.contains(protectedIh)) {
    530                            throw new StructuralCodeConstraintException("Subroutine instruction '" + protectedIh + "' is protected by an exception handler, '"
    531                                + handler + "'. This is forbidden by the JustIce verifier due to its clear definition of subroutines.");
    532                        }
    533                    }
    534                    protectedIh = protectedIh.getNext();
    535                }
    536            }
    537        }
    538
    539        // Now make sure no subroutine is calling a subroutine
    540        // that uses the same local variable for the RET as themselves
    541        // (recursively).
    542        // This includes that subroutines may not call themselves
    543        // recursively, even not through intermediate calls to other
    544        // subroutines.
    545        noRecursiveCalls(getTopLevel(), new HashSet<>());
    546
    547    }
    548
    549    /**
    550     * Returns the Subroutine object associated with the given leader (that is, the first instruction of the subroutine).
    551     * You must not use this to get the top-level instructions modeled as a Subroutine object.
    552     *
    553     * @see #getTopLevel()
    554     */
    555    public Subroutine getSubroutine(final InstructionHandle leader) {
    556        final Subroutine ret = subroutines.get(leader);
    557
    558        if (ret == null) {
    559            throw new AssertionViolatedException("Subroutine requested for an InstructionHandle that is not a leader of a subroutine.");
    560        }
    561
    562        if (ret == TOPLEVEL) {
    563            throw new AssertionViolatedException("TOPLEVEL special subroutine requested; use getTopLevel().");
    564        }
    565
    566        return ret;
    567    }
    568
    569    /**
    570     * For easy handling, the piece of code that is <B>not</B> a subroutine, the top-level, is also modeled as a Subroutine
    571     * object. It is a special Subroutine object where <B>you must not invoke getEnteringJsrInstructions() or
    572     * getLeavingRET()</B>.
    573     *
    574     * @see Subroutine#getEnteringJsrInstructions()
    575     * @see Subroutine#getLeavingRET()
    576     */
    577    public Subroutine getTopLevel() {
    578        return TOPLEVEL;
    579    }
    580
    581    /**
    582     * This (recursive) utility method makes sure that no subroutine is calling a subroutine that uses the same local
    583     * variable for the RET as themselves (recursively). This includes that subroutines may not call themselves recursively,
    584     * even not through intermediate calls to other subroutines.
    585     *
    586     * @throws StructuralCodeConstraintException if the above constraint is not satisfied.
    587     */
    588    private void noRecursiveCalls(final Subroutine sub, final Set<Integer> set) {
    589        final Subroutine[] subs = sub.subSubs();
    590
    591        for (final Subroutine sub2 : subs) {
    592            final int index = ((RET) sub2.getLeavingRET().getInstruction()).getIndex();
    593
    594            if (!set.add(Integer.valueOf(index))) {
    595                // Don't use toString() here because of possibly infinite recursive subSubs() calls then.
    596                final SubroutineImpl si = (SubroutineImpl) sub2;
    597                throw new StructuralCodeConstraintException("Subroutine with local variable '" + si.localVariable + "', JSRs '" + si.theJSRs + "', RET '"
    598                    + si.theRET + "' is called by a subroutine which uses the same local variable index as itself; maybe even a recursive call?"
    599                    + " JustIce's clean definition of a subroutine forbids both.");
    600            }
    601
    602            noRecursiveCalls(sub2, set);
    603
    604            set.remove(Integer.valueOf(index));
    605        }
    606    }
    607
    608    /**
    609     * Returns the subroutine object associated with the given instruction. This is a costly operation, you should consider
    610     * using getSubroutine(InstructionHandle). Returns 'null' if the given InstructionHandle lies in so-called 'dead code',
    611     * i.e. code that can never be executed.
    612     *
    613     * @see #getSubroutine(InstructionHandle)
    614     * @see #getTopLevel()
    615     */
    616    public Subroutine subroutineOf(final InstructionHandle any) {
    617        for (final Subroutine s : subroutines.values()) {
    618            if (s.contains(any)) {
    619                return s;
    620            }
    621        }
    622        System.err.println("DEBUG: Please verify '" + any.toString(true) + "' lies in dead code.");
    623        return null;
    624        // throw new AssertionViolatedException("No subroutine for InstructionHandle found (DEAD CODE?).");
    625    }
    626
    627    /**
    628     * Returns a String representation of this object; merely for debugging puposes.
    629     */
    630    @Override
    631    public String toString() {
    632        return "---\n" + subroutines + "\n---\n";
    633    }
    634}