1 /*

     2  * Copyright (c) 2008, 2015, Oracle and/or its affiliates. All rights reserved.

     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

     5  * This code is free software; you can redistribute it and/or modify it

     6  * under the terms of the GNU General Public License version 2 only, as

     7  * published by the Free Software Foundation.  Oracle designates this

     8  * particular file as subject to the "Classpath" exception as provided

     9  * by Oracle in the LICENSE file that accompanied this code.

    10  *

    11  * This code is distributed in the hope that it will be useful, but WITHOUT

    12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    14  * version 2 for more details (a copy is included in the LICENSE file that

    15  * accompanied this code).

    16  *

    17  * You should have received a copy of the GNU General Public License version

    18  * 2 along with this work; if not, write to the Free Software Foundation,

    19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    20  *

    21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

    22  * or visit www.oracle.com if you need additional information or have any

    23  * questions.

    24  */

    25 

    26 package java.lang.invoke;

    27 

    28 import jdk.internal.ref.CleanerFactory;

    29 import sun.invoke.util.Wrapper;

    30 

    31 import java.lang.invoke.MethodHandles.Lookup;

    32 import java.lang.reflect.Field;

    33 

    34 import static java.lang.invoke.MethodHandleNatives.Constants.*;

    35 import static java.lang.invoke.MethodHandleStatics.TRACE_METHOD_LINKAGE;

    36 import static java.lang.invoke.MethodHandles.Lookup.IMPL_LOOKUP;

    37 

    38 /**

    39  * The JVM interface for the method handles package is all here.

    40  * This is an interface internal and private to an implementation of JSR 292.

    41  * <em>This class is not part of the JSR 292 standard.</em>

    42  * @author jrose

    43  */

    44 class MethodHandleNatives {

    45 

    46     private MethodHandleNatives() { } // static only

    47 

    48     /// MemberName support

    49 

    50     static native void init(MemberName self, Object ref);

    51     static native void expand(MemberName self);

    52     static native MemberName resolve(MemberName self, Class<?> caller) throws LinkageError, ClassNotFoundException;

    53     static native int getMembers(Class<?> defc, String matchName, String matchSig,

    54             int matchFlags, Class<?> caller, int skip, MemberName[] results);

    55 

    56     /// Field layout queries parallel to jdk.internal.misc.Unsafe:

    57     static native long objectFieldOffset(MemberName self);  // e.g., returns vmindex

    58     static native long staticFieldOffset(MemberName self);  // e.g., returns vmindex

    59     static native Object staticFieldBase(MemberName self);  // e.g., returns clazz

    60     static native Object getMemberVMInfo(MemberName self);  // returns {vmindex,vmtarget}

    61 

    62     /// CallSite support

    63 

    64     /** Tell the JVM that we need to change the target of a CallSite. */

    65     static native void setCallSiteTargetNormal(CallSite site, MethodHandle target);

    66     static native void setCallSiteTargetVolatile(CallSite site, MethodHandle target);

    67 

    68     /** Represents a context to track nmethod dependencies on CallSite instance target. */

    69     static class CallSiteContext implements Runnable {

    70         //@Injected JVM_nmethodBucket* vmdependencies;

    71 

    72         static CallSiteContext make(CallSite cs) {

    73             final CallSiteContext newContext = new CallSiteContext();

    74             // CallSite instance is tracked by a Cleanable which clears native

    75             // structures allocated for CallSite context. Though the CallSite can

    76             // become unreachable, its Context is retained by the Cleanable instance

    77             // (which is referenced from Cleaner instance which is referenced from

    78             // CleanerFactory class) until cleanup is performed.

    79             CleanerFactory.cleaner().register(cs, newContext);

    80             return newContext;

    81         }

    82 

    83         @Override

    84         public void run() {

    85             MethodHandleNatives.clearCallSiteContext(this);

    86         }

    87     }

    88 

    89     /** Invalidate all recorded nmethods. */

    90     private static native void clearCallSiteContext(CallSiteContext context);

    91 

    92     private static native void registerNatives();

    93     static {

    94         registerNatives();

    95     }

    96 

    97     /**

    98      * Compile-time constants go here. This collection exists not only for

    99      * reference from clients, but also for ensuring the VM and JDK agree on the

   100      * values of these constants (see {@link #verifyConstants()}).

   101      */

   102     static class Constants {

   103         Constants() { } // static only

   104 

   105         static final int

   106             MN_IS_METHOD           = 0x00010000, // method (not constructor)

   107             MN_IS_CONSTRUCTOR      = 0x00020000, // constructor

   108             MN_IS_FIELD            = 0x00040000, // field

   109             MN_IS_TYPE             = 0x00080000, // nested type

   110             MN_CALLER_SENSITIVE    = 0x00100000, // @CallerSensitive annotation detected

   111             MN_REFERENCE_KIND_SHIFT = 24, // refKind

   112             MN_REFERENCE_KIND_MASK = 0x0F000000 >> MN_REFERENCE_KIND_SHIFT,

   113             // The SEARCH_* bits are not for MN.flags but for the matchFlags argument of MHN.getMembers:

   114             MN_SEARCH_SUPERCLASSES = 0x00100000,

   115             MN_SEARCH_INTERFACES   = 0x00200000;

   116 

   117         /**

   118          * Constant pool reference-kind codes, as used by CONSTANT_MethodHandle CP entries.

   119          */

   120         static final byte

   121             REF_NONE                    = 0,  // null value

   122             REF_getField                = 1,

   123             REF_getStatic               = 2,

   124             REF_putField                = 3,

   125             REF_putStatic               = 4,

   126             REF_invokeVirtual           = 5,

   127             REF_invokeStatic            = 6,

   128             REF_invokeSpecial           = 7,

   129             REF_newInvokeSpecial        = 8,

   130             REF_invokeInterface         = 9,

   131             REF_LIMIT                  = 10;

   132     }

   133 

   134     static boolean refKindIsValid(int refKind) {

   135         return (refKind > REF_NONE && refKind < REF_LIMIT);

   136     }

   137     static boolean refKindIsField(byte refKind) {

   138         assert(refKindIsValid(refKind));

   139         return (refKind <= REF_putStatic);

   140     }

   141     static boolean refKindIsGetter(byte refKind) {

   142         assert(refKindIsValid(refKind));

   143         return (refKind <= REF_getStatic);

   144     }

   145     static boolean refKindIsSetter(byte refKind) {

   146         return refKindIsField(refKind) && !refKindIsGetter(refKind);

   147     }

   148     static boolean refKindIsMethod(byte refKind) {

   149         return !refKindIsField(refKind) && (refKind != REF_newInvokeSpecial);

   150     }

   151     static boolean refKindIsConstructor(byte refKind) {

   152         return (refKind == REF_newInvokeSpecial);

   153     }

   154     static boolean refKindHasReceiver(byte refKind) {

   155         assert(refKindIsValid(refKind));

   156         return (refKind & 1) != 0;

   157     }

   158     static boolean refKindIsStatic(byte refKind) {

   159         return !refKindHasReceiver(refKind) && (refKind != REF_newInvokeSpecial);

   160     }

   161     static boolean refKindDoesDispatch(byte refKind) {

   162         assert(refKindIsValid(refKind));

   163         return (refKind == REF_invokeVirtual ||

   164                 refKind == REF_invokeInterface);

   165     }

   166     static {

   167         final int HR_MASK = ((1 << REF_getField) |

   168                              (1 << REF_putField) |

   169                              (1 << REF_invokeVirtual) |

   170                              (1 << REF_invokeSpecial) |

   171                              (1 << REF_invokeInterface)

   172                             );

   173         for (byte refKind = REF_NONE+1; refKind < REF_LIMIT; refKind++) {

   174             assert(refKindHasReceiver(refKind) == (((1<<refKind) & HR_MASK) != 0)) : refKind;

   175         }

   176     }

   177     static String refKindName(byte refKind) {

   178         assert(refKindIsValid(refKind));

   179         switch (refKind) {

   180         case REF_getField:          return "getField";

   181         case REF_getStatic:         return "getStatic";

   182         case REF_putField:          return "putField";

   183         case REF_putStatic:         return "putStatic";

   184         case REF_invokeVirtual:     return "invokeVirtual";

   185         case REF_invokeStatic:      return "invokeStatic";

   186         case REF_invokeSpecial:     return "invokeSpecial";

   187         case REF_newInvokeSpecial:  return "newInvokeSpecial";

   188         case REF_invokeInterface:   return "invokeInterface";

   189         default:                    return "REF_???";

   190         }

   191     }

   192 

   193     private static native int getNamedCon(int which, Object[] name);

   194     static boolean verifyConstants() {

   195         Object[] box = { null };

   196         for (int i = 0; ; i++) {

   197             box[0] = null;

   198             int vmval = getNamedCon(i, box);

   199             if (box[0] == null)  break;

   200             String name = (String) box[0];

   201             try {

   202                 Field con = Constants.class.getDeclaredField(name);

   203                 int jval = con.getInt(null);

   204                 if (jval == vmval)  continue;

   205                 String err = (name+": JVM has "+vmval+" while Java has "+jval);

   206                 if (name.equals("CONV_OP_LIMIT")) {

   207                     System.err.println("warning: "+err);

   208                     continue;

   209                 }

   210                 throw new InternalError(err);

   211             } catch (NoSuchFieldException | IllegalAccessException ex) {

   212                 String err = (name+": JVM has "+vmval+" which Java does not define");

   213                 // ignore exotic ops the JVM cares about; we just wont issue them

   214                 //System.err.println("warning: "+err);

   215                 continue;

   216             }

   217         }

   218         return true;

   219     }

   220     static {

   221         assert(verifyConstants());

   222     }

   223 

   224     // Up-calls from the JVM.

   225     // These must NOT be public.

   226 

   227     /**

   228      * The JVM is linking an invokedynamic instruction.  Create a reified call site for it.

   229      */

   230     static MemberName linkCallSite(Object callerObj,

   231                                    Object bootstrapMethodObj,

   232                                    Object nameObj, Object typeObj,

   233                                    Object staticArguments,

   234                                    Object[] appendixResult) {

   235         MethodHandle bootstrapMethod = (MethodHandle)bootstrapMethodObj;

   236         Class<?> caller = (Class<?>)callerObj;

   237         String name = nameObj.toString().intern();

   238         MethodType type = (MethodType)typeObj;

   239         if (!TRACE_METHOD_LINKAGE)

   240             return linkCallSiteImpl(caller, bootstrapMethod, name, type,

   241                                     staticArguments, appendixResult);

   242         return linkCallSiteTracing(caller, bootstrapMethod, name, type,

   243                                    staticArguments, appendixResult);

   244     }

   245     static MemberName linkCallSiteImpl(Class<?> caller,

   246                                        MethodHandle bootstrapMethod,

   247                                        String name, MethodType type,

   248                                        Object staticArguments,

   249                                        Object[] appendixResult) {

   250         CallSite callSite = CallSite.makeSite(bootstrapMethod,

   251                                               name,

   252                                               type,

   253                                               staticArguments,

   254                                               caller);

   255         if (callSite instanceof ConstantCallSite) {

   256             appendixResult[0] = callSite.dynamicInvoker();

   257             return Invokers.linkToTargetMethod(type);

   258         } else {

   259             appendixResult[0] = callSite;

   260             return Invokers.linkToCallSiteMethod(type);

   261         }

   262     }

   263     // Tracing logic:

   264     static MemberName linkCallSiteTracing(Class<?> caller,

   265                                           MethodHandle bootstrapMethod,

   266                                           String name, MethodType type,

   267                                           Object staticArguments,

   268                                           Object[] appendixResult) {

   269         Object bsmReference = bootstrapMethod.internalMemberName();

   270         if (bsmReference == null)  bsmReference = bootstrapMethod;

   271         Object staticArglist = (staticArguments instanceof Object[] ?

   272                                 java.util.Arrays.asList((Object[]) staticArguments) :

   273                                 staticArguments);

   274         System.out.println("linkCallSite "+caller.getName()+" "+

   275                            bsmReference+" "+

   276                            name+type+"/"+staticArglist);

   277         try {

   278             MemberName res = linkCallSiteImpl(caller, bootstrapMethod, name, type,

   279                                               staticArguments, appendixResult);

   280             System.out.println("linkCallSite => "+res+" + "+appendixResult[0]);

   281             return res;

   282         } catch (Throwable ex) {

   283             System.out.println("linkCallSite => throw "+ex);

   284             throw ex;

   285         }

   286     }

   287 

   288     /**

   289      * The JVM wants a pointer to a MethodType.  Oblige it by finding or creating one.

   290      */

   291     static MethodType findMethodHandleType(Class<?> rtype, Class<?>[] ptypes) {

   292         return MethodType.makeImpl(rtype, ptypes, true);

   293     }

   294 

   295     /**

   296      * The JVM wants to link a call site that requires a dynamic type check.

   297      * Name is a type-checking invoker, invokeExact or invoke.

   298      * Return a JVM method (MemberName) to handle the invoking.

   299      * The method assumes the following arguments on the stack:

   300      * 0: the method handle being invoked

   301      * 1-N: the arguments to the method handle invocation

   302      * N+1: an optional, implicitly added argument (typically the given MethodType)

   303      * <p>

   304      * The nominal method at such a call site is an instance of

   305      * a signature-polymorphic method (see @PolymorphicSignature).

   306      * Such method instances are user-visible entities which are

   307      * "split" from the generic placeholder method in {@code MethodHandle}.

   308      * (Note that the placeholder method is not identical with any of

   309      * its instances.  If invoked reflectively, is guaranteed to throw an

   310      * {@code UnsupportedOperationException}.)

   311      * If the signature-polymorphic method instance is ever reified,

   312      * it appears as a "copy" of the original placeholder

   313      * (a native final member of {@code MethodHandle}) except

   314      * that its type descriptor has shape required by the instance,

   315      * and the method instance is <em>not</em> varargs.

   316      * The method instance is also marked synthetic, since the

   317      * method (by definition) does not appear in Java source code.

   318      * <p>

   319      * The JVM is allowed to reify this method as instance metadata.

   320      * For example, {@code invokeBasic} is always reified.

   321      * But the JVM may instead call {@code linkMethod}.

   322      * If the result is an * ordered pair of a {@code (method, appendix)},

   323      * the method gets all the arguments (0..N inclusive)

   324      * plus the appendix (N+1), and uses the appendix to complete the call.

   325      * In this way, one reusable method (called a "linker method")

   326      * can perform the function of any number of polymorphic instance

   327      * methods.

   328      * <p>

   329      * Linker methods are allowed to be weakly typed, with any or

   330      * all references rewritten to {@code Object} and any primitives

   331      * (except {@code long}/{@code float}/{@code double})

   332      * rewritten to {@code int}.

   333      * A linker method is trusted to return a strongly typed result,

   334      * according to the specific method type descriptor of the

   335      * signature-polymorphic instance it is emulating.

   336      * This can involve (as necessary) a dynamic check using

   337      * data extracted from the appendix argument.

   338      * <p>

   339      * The JVM does not inspect the appendix, other than to pass

   340      * it verbatim to the linker method at every call.

   341      * This means that the JDK runtime has wide latitude

   342      * for choosing the shape of each linker method and its

   343      * corresponding appendix.

   344      * Linker methods should be generated from {@code LambdaForm}s

   345      * so that they do not become visible on stack traces.

   346      * <p>

   347      * The {@code linkMethod} call is free to omit the appendix

   348      * (returning null) and instead emulate the required function

   349      * completely in the linker method.

   350      * As a corner case, if N==255, no appendix is possible.

   351      * In this case, the method returned must be custom-generated to

   352      * to perform any needed type checking.

   353      * <p>

   354      * If the JVM does not reify a method at a call site, but instead

   355      * calls {@code linkMethod}, the corresponding call represented

   356      * in the bytecodes may mention a valid method which is not

   357      * representable with a {@code MemberName}.

   358      * Therefore, use cases for {@code linkMethod} tend to correspond to

   359      * special cases in reflective code such as {@code findVirtual}

   360      * or {@code revealDirect}.

   361      */

   362     static MemberName linkMethod(Class<?> callerClass, int refKind,

   363                                  Class<?> defc, String name, Object type,

   364                                  Object[] appendixResult) {

   365         if (!TRACE_METHOD_LINKAGE)

   366             return linkMethodImpl(callerClass, refKind, defc, name, type, appendixResult);

   367         return linkMethodTracing(callerClass, refKind, defc, name, type, appendixResult);

   368     }

   369     static MemberName linkMethodImpl(Class<?> callerClass, int refKind,

   370                                      Class<?> defc, String name, Object type,

   371                                      Object[] appendixResult) {

   372         try {

   373             if (refKind == REF_invokeVirtual) {

   374                 if (defc == MethodHandle.class) {

   375                     return Invokers.methodHandleInvokeLinkerMethod(

   376                             name, fixMethodType(callerClass, type), appendixResult);

   377                 } else if (defc == VarHandle.class) {

   378                     return varHandleOperationLinkerMethod(

   379                             name, fixMethodType(callerClass, type), appendixResult);

   380                 }

   381             }

   382         } catch (Error e) {

   383             // Pass through an Error, including say StackOverflowError or

   384             // OutOfMemoryError

   385             throw e;

   386         } catch (Throwable ex) {

   387             // Wrap anything else in LinkageError

   388             throw new LinkageError(ex.getMessage(), ex);

   389         }

   390         throw new LinkageError("no such method "+defc.getName()+"."+name+type);

   391     }

   392     private static MethodType fixMethodType(Class<?> callerClass, Object type) {

   393         if (type instanceof MethodType)

   394             return (MethodType) type;

   395         else

   396             return MethodType.fromDescriptor((String)type, callerClass.getClassLoader());

   397     }

   398     // Tracing logic:

   399     static MemberName linkMethodTracing(Class<?> callerClass, int refKind,

   400                                         Class<?> defc, String name, Object type,

   401                                         Object[] appendixResult) {

   402         System.out.println("linkMethod "+defc.getName()+"."+

   403                            name+type+"/"+Integer.toHexString(refKind));

   404         try {

   405             MemberName res = linkMethodImpl(callerClass, refKind, defc, name, type, appendixResult);

   406             System.out.println("linkMethod => "+res+" + "+appendixResult[0]);

   407             return res;

   408         } catch (Throwable ex) {

   409             System.out.println("linkMethod => throw "+ex);

   410             throw ex;

   411         }

   412     }

   413 

   414     /**

   415      * Obtain the method to link to the VarHandle operation.

   416      * This method is located here and not in Invokers to avoid

   417      * intializing that and other classes early on in VM bootup.

   418      */

   419     private static MemberName varHandleOperationLinkerMethod(String name,

   420                                                              MethodType mtype,

   421                                                              Object[] appendixResult) {

   422         // Get the signature method type

   423         final MethodType sigType = mtype.basicType();

   424 

   425         // Get the access kind from the method name

   426         VarHandle.AccessMode ak;

   427         try {

   428             ak = VarHandle.AccessMode.valueFromMethodName(name);

   429         } catch (IllegalArgumentException e) {

   430             throw MethodHandleStatics.newInternalError(e);

   431         }

   432 

   433         // Create the appendix descriptor constant

   434         VarHandle.AccessDescriptor ad = new VarHandle.AccessDescriptor(mtype, ak.at.ordinal(), ak.ordinal());

   435         appendixResult[0] = ad;

   436 

   437         if (MethodHandleStatics.VAR_HANDLE_GUARDS) {

   438             // If not polymorphic in the return type, such as the compareAndSet

   439             // methods that return boolean

   440             Class<?> guardReturnType = sigType.returnType();

   441             if (ak.at.isMonomorphicInReturnType) {

   442                 if (ak.at.returnType != mtype.returnType()) {

   443                     // The caller contains a different return type than that

   444                     // defined by the method

   445                     throw newNoSuchMethodErrorOnVarHandle(name, mtype);

   446                 }

   447                 // Adjust the return type of the signature method type

   448                 guardReturnType = ak.at.returnType;

   449             }

   450 

   451             // Get the guard method type for linking

   452             final Class<?>[] guardParams = new Class<?>[sigType.parameterCount() + 2];

   453             // VarHandle at start

   454             guardParams[0] = VarHandle.class;

   455             for (int i = 0; i < sigType.parameterCount(); i++) {

   456                 guardParams[i + 1] = sigType.parameterType(i);

   457             }

   458             // Access descriptor at end

   459             guardParams[guardParams.length - 1] = VarHandle.AccessDescriptor.class;

   460             MethodType guardType = MethodType.makeImpl(guardReturnType, guardParams, true);

   461 

   462             MemberName linker = new MemberName(

   463                     VarHandleGuards.class, getVarHandleGuardMethodName(guardType),

   464                     guardType, REF_invokeStatic);

   465 

   466             linker = MemberName.getFactory().resolveOrNull(REF_invokeStatic, linker,

   467                                                            VarHandleGuards.class);

   468             if (linker != null) {

   469                 return linker;

   470             }

   471             // Fall back to lambda form linkage if guard method is not available

   472             // TODO Optionally log fallback ?

   473         }

   474         return Invokers.varHandleInvokeLinkerMethod(ak, mtype);

   475     }

   476     static String getVarHandleGuardMethodName(MethodType guardType) {

   477         String prefix = "guard_";

   478         StringBuilder sb = new StringBuilder(prefix.length() + guardType.parameterCount());

   479 

   480         sb.append(prefix);

   481         for (int i = 1; i < guardType.parameterCount() - 1; i++) {

   482             Class<?> pt = guardType.parameterType(i);

   483             sb.append(getCharType(pt));

   484         }

   485         sb.append('_').append(getCharType(guardType.returnType()));

   486         return sb.toString();

   487     }

   488     static char getCharType(Class<?> pt) {

   489         return Wrapper.forBasicType(pt).basicTypeChar();

   490     }

   491     static NoSuchMethodError newNoSuchMethodErrorOnVarHandle(String name, MethodType mtype) {

   492         return new NoSuchMethodError("VarHandle." + name + mtype);

   493     }

   494 

   495     /**

   496      * The JVM is resolving a CONSTANT_MethodHandle CP entry.  And it wants our help.

   497      * It will make an up-call to this method.  (Do not change the name or signature.)

   498      * The type argument is a Class for field requests and a MethodType for non-fields.

   499      * <p>

   500      * Recent versions of the JVM may also pass a resolved MemberName for the type.

   501      * In that case, the name is ignored and may be null.

   502      */

   503     static MethodHandle linkMethodHandleConstant(Class<?> callerClass, int refKind,

   504                                                  Class<?> defc, String name, Object type) {

   505         try {

   506             Lookup lookup = IMPL_LOOKUP.in(callerClass);

   507             assert(refKindIsValid(refKind));

   508             return lookup.linkMethodHandleConstant((byte) refKind, defc, name, type);

   509         } catch (IllegalAccessException ex) {

   510             Throwable cause = ex.getCause();

   511             if (cause instanceof AbstractMethodError) {

   512                 throw (AbstractMethodError) cause;

   513             } else {

   514                 Error err = new IllegalAccessError(ex.getMessage());

   515                 throw initCauseFrom(err, ex);

   516             }

   517         } catch (NoSuchMethodException ex) {

   518             Error err = new NoSuchMethodError(ex.getMessage());

   519             throw initCauseFrom(err, ex);

   520         } catch (NoSuchFieldException ex) {

   521             Error err = new NoSuchFieldError(ex.getMessage());

   522             throw initCauseFrom(err, ex);

   523         } catch (ReflectiveOperationException ex) {

   524             Error err = new IncompatibleClassChangeError();

   525             throw initCauseFrom(err, ex);

   526         }

   527     }

   528 

   529     /**

   530      * Use best possible cause for err.initCause(), substituting the

   531      * cause for err itself if the cause has the same (or better) type.

   532      */

   533     private static Error initCauseFrom(Error err, Exception ex) {

   534         Throwable th = ex.getCause();

   535         if (err.getClass().isInstance(th))

   536            return (Error) th;

   537         err.initCause(th == null ? ex : th);

   538         return err;

   539     }

   540 

   541     /**

   542      * Is this method a caller-sensitive method?

   543      * I.e., does it call Reflection.getCallerClass or a similar method

   544      * to ask about the identity of its caller?

   545      */

   546     static boolean isCallerSensitive(MemberName mem) {

   547         if (!mem.isInvocable())  return false;  // fields are not caller sensitive

   548 

   549         return mem.isCallerSensitive() || canBeCalledVirtual(mem);

   550     }

   551 

   552     static boolean canBeCalledVirtual(MemberName mem) {

   553         assert(mem.isInvocable());

   554         Class<?> defc = mem.getDeclaringClass();

   555         switch (mem.getName()) {

   556         case "checkMemberAccess":

   557             return canBeCalledVirtual(mem, java.lang.SecurityManager.class);

   558         case "getContextClassLoader":

   559             return canBeCalledVirtual(mem, java.lang.Thread.class);

   560         }

   561         return false;

   562     }

   563 

   564     static boolean canBeCalledVirtual(MemberName symbolicRef, Class<?> definingClass) {

   565         Class<?> symbolicRefClass = symbolicRef.getDeclaringClass();

   566         if (symbolicRefClass == definingClass)  return true;

   567         if (symbolicRef.isStatic() || symbolicRef.isPrivate())  return false;

   568         return (definingClass.isAssignableFrom(symbolicRefClass) ||  // Msym overrides Mdef

   569                 symbolicRefClass.isInterface());                     // Mdef implements Msym

   570     }

   571 }