1 /*
  2  * Copyright (c) 2008, 2021, 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.misc.VM;
 29 import jdk.internal.ref.CleanerFactory;
 30 import sun.invoke.util.Wrapper;
 31 
 32 import java.lang.invoke.MethodHandles.Lookup;
 33 import java.lang.reflect.Field;
 34 
 35 import static java.lang.invoke.MethodHandleNatives.Constants.*;
 36 import static java.lang.invoke.MethodHandleStatics.TRACE_METHOD_LINKAGE;
 37 import static java.lang.invoke.MethodHandles.Lookup.IMPL_LOOKUP;
 38 
 39 /**
 40  * The JVM interface for the method handles package is all here.
 41  * This is an interface internal and private to an implementation of JSR 292.
 42  * <em>This class is not part of the JSR 292 standard.</em>
 43  * @author jrose
 44  */
 45 class MethodHandleNatives {
 46 
 47     private MethodHandleNatives() { } // static only
 48 
 49     /// MemberName support
 50 
 51     static native void init(MemberName self, Object ref);
 52     static native void expand(MemberName self);
 53     static native MemberName resolve(MemberName self, Class<?> caller, int lookupMode,
 54             boolean speculativeResolve) throws LinkageError, ClassNotFoundException;
 55     static native int getMembers(Class<?> defc, String matchName, String matchSig,
 56             int matchFlags, Class<?> caller, int skip, MemberName[] results);
 57 
 58     /// Field layout queries parallel to jdk.internal.misc.Unsafe:
 59     static native long objectFieldOffset(MemberName self);  // e.g., returns vmindex
 60     static native long staticFieldOffset(MemberName self);  // e.g., returns vmindex
 61     static native Object staticFieldBase(MemberName self);  // e.g., returns clazz
 62     static native Object getMemberVMInfo(MemberName self);  // returns {vmindex,vmtarget}
 63 
 64     /// CallSite support
 65 
 66     /** Tell the JVM that we need to change the target of a CallSite. */
 67     static native void setCallSiteTargetNormal(CallSite site, MethodHandle target);
 68     static native void setCallSiteTargetVolatile(CallSite site, MethodHandle target);
 69 
 70     static native void copyOutBootstrapArguments(Class<?> caller, int[] indexInfo,
 71                                                  int start, int end,
 72                                                  Object[] buf, int pos,
 73                                                  boolean resolve,
 74                                                  Object ifNotAvailable);
 75 
 76     /** Represents a context to track nmethod dependencies on CallSite instance target. */
 77     static class CallSiteContext implements Runnable {
 78         //@Injected JVM_nmethodBucket* vmdependencies;
 79         //@Injected jlong last_cleanup;
 80 
 81         static CallSiteContext make(CallSite cs) {
 82             final CallSiteContext newContext = new CallSiteContext();
 83             // CallSite instance is tracked by a Cleanable which clears native
 84             // structures allocated for CallSite context. Though the CallSite can
 85             // become unreachable, its Context is retained by the Cleanable instance
 86             // (which is referenced from Cleaner instance which is referenced from
 87             // CleanerFactory class) until cleanup is performed.
 88             CleanerFactory.cleaner().register(cs, newContext);
 89             return newContext;
 90         }
 91 
 92         @Override
 93         public void run() {
 94             MethodHandleNatives.clearCallSiteContext(this);
 95         }
 96     }
 97 
 98     /** Invalidate all recorded nmethods. */
 99     private static native void clearCallSiteContext(CallSiteContext context);
100 
101     private static native void registerNatives();
102     static {
103         registerNatives();
104     }
105 
106     /**
107      * Compile-time constants go here. This collection exists not only for
108      * reference from clients, but also for ensuring the VM and JDK agree on the
109      * values of these constants (see {@link #verifyConstants()}).
110      */
111     static class Constants {
112         Constants() { } // static only
113 
114         static final int
115             MN_IS_METHOD           = 0x00010000, // method (not constructor)
116             MN_IS_CONSTRUCTOR      = 0x00020000, // constructor
117             MN_IS_FIELD            = 0x00040000, // field
118             MN_IS_TYPE             = 0x00080000, // nested type
119             MN_CALLER_SENSITIVE    = 0x00100000, // @CallerSensitive annotation detected
120             MN_TRUSTED_FINAL       = 0x00200000, // trusted final field
121             MN_REFERENCE_KIND_SHIFT = 24, // refKind
122             MN_REFERENCE_KIND_MASK = 0x0F000000 >> MN_REFERENCE_KIND_SHIFT,

123             // The SEARCH_* bits are not for MN.flags but for the matchFlags argument of MHN.getMembers:
124             MN_SEARCH_SUPERCLASSES = 0x00100000,
125             MN_SEARCH_INTERFACES   = 0x00200000;
126 
127         /**
128          * Constant pool reference-kind codes, as used by CONSTANT_MethodHandle CP entries.
129          */
130         static final byte
131             REF_NONE                    = 0,  // null value
132             REF_getField                = 1,
133             REF_getStatic               = 2,
134             REF_putField                = 3,
135             REF_putStatic               = 4,
136             REF_invokeVirtual           = 5,
137             REF_invokeStatic            = 6,
138             REF_invokeSpecial           = 7,
139             REF_newInvokeSpecial        = 8,
140             REF_invokeInterface         = 9,
141             REF_LIMIT                  = 10;
142 
143         /**
144          * Flags for Lookup.ClassOptions
145          */
146         static final int
147             NESTMATE_CLASS            = 0x00000001,
148             HIDDEN_CLASS              = 0x00000002,
149             STRONG_LOADER_LINK        = 0x00000004,
150             ACCESS_VM_ANNOTATIONS     = 0x00000008;
151 
152         /**
153          * Lookup modes
154          */
155         static final int
156             LM_MODULE        = Lookup.MODULE,
157             LM_UNCONDITIONAL = Lookup.UNCONDITIONAL,
158             LM_TRUSTED       = -1;
159 
160     }
161 
162     static boolean refKindIsValid(int refKind) {
163         return (refKind > REF_NONE && refKind < REF_LIMIT);
164     }
165     static boolean refKindIsField(byte refKind) {
166         assert(refKindIsValid(refKind));
167         return (refKind <= REF_putStatic);
168     }
169     static boolean refKindIsGetter(byte refKind) {
170         assert(refKindIsValid(refKind));
171         return (refKind <= REF_getStatic);
172     }
173     static boolean refKindIsSetter(byte refKind) {
174         return refKindIsField(refKind) && !refKindIsGetter(refKind);
175     }
176     static boolean refKindIsMethod(byte refKind) {
177         return !refKindIsField(refKind) && (refKind != REF_newInvokeSpecial);
178     }
179     static boolean refKindIsConstructor(byte refKind) {
180         return (refKind == REF_newInvokeSpecial);
181     }
182     static boolean refKindHasReceiver(byte refKind) {
183         assert(refKindIsValid(refKind));
184         return (refKind & 1) != 0;
185     }
186     static boolean refKindIsStatic(byte refKind) {
187         return !refKindHasReceiver(refKind) && (refKind != REF_newInvokeSpecial);
188     }
189     static boolean refKindDoesDispatch(byte refKind) {
190         assert(refKindIsValid(refKind));
191         return (refKind == REF_invokeVirtual ||
192                 refKind == REF_invokeInterface);
193     }
194     static {
195         final int HR_MASK = ((1 << REF_getField) |
196                              (1 << REF_putField) |
197                              (1 << REF_invokeVirtual) |
198                              (1 << REF_invokeSpecial) |
199                              (1 << REF_invokeInterface)
200                             );
201         for (byte refKind = REF_NONE+1; refKind < REF_LIMIT; refKind++) {
202             assert(refKindHasReceiver(refKind) == (((1<<refKind) & HR_MASK) != 0)) : refKind;
203         }
204     }
205     static String refKindName(byte refKind) {
206         assert(refKindIsValid(refKind));
207         return switch (refKind) {
208             case REF_getField         -> "getField";
209             case REF_getStatic        -> "getStatic";
210             case REF_putField         -> "putField";
211             case REF_putStatic        -> "putStatic";
212             case REF_invokeVirtual    -> "invokeVirtual";
213             case REF_invokeStatic     -> "invokeStatic";
214             case REF_invokeSpecial    -> "invokeSpecial";
215             case REF_newInvokeSpecial -> "newInvokeSpecial";
216             case REF_invokeInterface  -> "invokeInterface";
217             default -> "REF_???";
218         };
219     }
220 
221     private static native int getNamedCon(int which, Object[] name);
222     static boolean verifyConstants() {
223         Object[] box = { null };
224         for (int i = 0; ; i++) {
225             box[0] = null;
226             int vmval = getNamedCon(i, box);
227             if (box[0] == null)  break;
228             String name = (String) box[0];
229             try {
230                 Field con = Constants.class.getDeclaredField(name);
231                 int jval = con.getInt(null);
232                 if (jval == vmval)  continue;
233                 String err = (name+": JVM has "+vmval+" while Java has "+jval);
234                 if (name.equals("CONV_OP_LIMIT")) {
235                     System.err.println("warning: "+err);
236                     continue;
237                 }
238                 throw new InternalError(err);
239             } catch (NoSuchFieldException | IllegalAccessException ex) {
240                 String err = (name+": JVM has "+vmval+" which Java does not define");
241                 // ignore exotic ops the JVM cares about; we just wont issue them
242                 //System.err.println("warning: "+err);
243                 continue;
244             }
245         }
246         return true;
247     }
248     static {
249         VM.setJavaLangInvokeInited();
250         assert(verifyConstants());
251     }
252 
253     // Up-calls from the JVM.
254     // These must NOT be public.
255 
256     /**
257      * The JVM is linking an invokedynamic instruction.  Create a reified call site for it.
258      */
259     static MemberName linkCallSite(Object callerObj,
260                                    Object bootstrapMethodObj,
261                                    Object nameObj, Object typeObj,
262                                    Object staticArguments,
263                                    Object[] appendixResult) {
264         MethodHandle bootstrapMethod = (MethodHandle)bootstrapMethodObj;
265         Class<?> caller = (Class<?>)callerObj;
266         String name = nameObj.toString().intern();
267         MethodType type = (MethodType)typeObj;
268         if (!TRACE_METHOD_LINKAGE)
269             return linkCallSiteImpl(caller, bootstrapMethod, name, type,
270                                     staticArguments, appendixResult);
271         return linkCallSiteTracing(caller, bootstrapMethod, name, type,
272                                    staticArguments, appendixResult);
273     }
274     static MemberName linkCallSiteImpl(Class<?> caller,
275                                        MethodHandle bootstrapMethod,
276                                        String name, MethodType type,
277                                        Object staticArguments,
278                                        Object[] appendixResult) {
279         CallSite callSite = CallSite.makeSite(bootstrapMethod,
280                                               name,
281                                               type,
282                                               staticArguments,
283                                               caller);
284         if (callSite instanceof ConstantCallSite) {
285             appendixResult[0] = callSite.dynamicInvoker();
286             return Invokers.linkToTargetMethod(type);
287         } else {
288             appendixResult[0] = callSite;
289             return Invokers.linkToCallSiteMethod(type);
290         }
291     }
292     // Tracing logic:
293     static MemberName linkCallSiteTracing(Class<?> caller,
294                                           MethodHandle bootstrapMethod,
295                                           String name, MethodType type,
296                                           Object staticArguments,
297                                           Object[] appendixResult) {
298         Object bsmReference = bootstrapMethod.internalMemberName();
299         if (bsmReference == null)  bsmReference = bootstrapMethod;
300         String staticArglist = staticArglistForTrace(staticArguments);
301         System.out.println("linkCallSite "+caller.getName()+" "+
302                            bsmReference+" "+
303                            name+type+"/"+staticArglist);
304         try {
305             MemberName res = linkCallSiteImpl(caller, bootstrapMethod, name, type,
306                                               staticArguments, appendixResult);
307             System.out.println("linkCallSite => "+res+" + "+appendixResult[0]);
308             return res;
309         } catch (Throwable ex) {
310             ex.printStackTrace(); // print now in case exception is swallowed
311             System.out.println("linkCallSite => throw "+ex);
312             throw ex;
313         }
314     }
315 
316     // this implements the upcall from the JVM, MethodHandleNatives.linkDynamicConstant:
317     static Object linkDynamicConstant(Object callerObj,
318                                       Object bootstrapMethodObj,
319                                       Object nameObj, Object typeObj,
320                                       Object staticArguments) {
321         MethodHandle bootstrapMethod = (MethodHandle)bootstrapMethodObj;
322         Class<?> caller = (Class<?>)callerObj;
323         String name = nameObj.toString().intern();
324         Class<?> type = (Class<?>)typeObj;
325         if (!TRACE_METHOD_LINKAGE)
326             return linkDynamicConstantImpl(caller, bootstrapMethod, name, type, staticArguments);
327         return linkDynamicConstantTracing(caller, bootstrapMethod, name, type, staticArguments);
328     }
329 
330     static Object linkDynamicConstantImpl(Class<?> caller,
331                                           MethodHandle bootstrapMethod,
332                                           String name, Class<?> type,
333                                           Object staticArguments) {
334         return ConstantBootstraps.makeConstant(bootstrapMethod, name, type, staticArguments, caller);
335     }
336 
337     private static String staticArglistForTrace(Object staticArguments) {
338         if (staticArguments instanceof Object[])
339             return "BSA="+java.util.Arrays.asList((Object[]) staticArguments);
340         if (staticArguments instanceof int[])
341             return "BSA@"+java.util.Arrays.toString((int[]) staticArguments);
342         if (staticArguments == null)
343             return "BSA0=null";
344         return "BSA1="+staticArguments;
345     }
346 
347     // Tracing logic:
348     static Object linkDynamicConstantTracing(Class<?> caller,
349                                              MethodHandle bootstrapMethod,
350                                              String name, Class<?> type,
351                                              Object staticArguments) {
352         Object bsmReference = bootstrapMethod.internalMemberName();
353         if (bsmReference == null)  bsmReference = bootstrapMethod;
354         String staticArglist = staticArglistForTrace(staticArguments);
355         System.out.println("linkDynamicConstant "+caller.getName()+" "+
356                            bsmReference+" "+
357                            name+type+"/"+staticArglist);
358         try {
359             Object res = linkDynamicConstantImpl(caller, bootstrapMethod, name, type, staticArguments);
360             System.out.println("linkDynamicConstantImpl => "+res);
361             return res;
362         } catch (Throwable ex) {
363             ex.printStackTrace(); // print now in case exception is swallowed
364             System.out.println("linkDynamicConstant => throw "+ex);
365             throw ex;
366         }
367     }
368 
369     /** The JVM is requesting pull-mode bootstrap when it provides
370      *  a tuple of the form int[]{ argc, vmindex }.
371      *  The BSM is expected to call back to the JVM using the caller
372      *  class and vmindex to resolve the static arguments.
373      */
374     static boolean staticArgumentsPulled(Object staticArguments) {
375         return staticArguments instanceof int[];
376     }
377 
378     /** A BSM runs in pull-mode if and only if its sole arguments
379      * are (Lookup, BootstrapCallInfo), or can be converted pairwise
380      * to those types, and it is not of variable arity.
381      * Excluding error cases, we can just test that the arity is a constant 2.
382      *
383      * NOTE: This method currently returns false, since pulling is not currently
384      * exposed to a BSM. When pull mode is supported the method block will be
385      * replaced with currently commented out code.
386      */
387     static boolean isPullModeBSM(MethodHandle bsm) {
388         return false;
389 //        return bsm.type().parameterCount() == 2 && !bsm.isVarargsCollector();
390     }
391 
392     /**
393      * The JVM wants a pointer to a MethodType.  Oblige it by finding or creating one.
394      */
395     static MethodType findMethodHandleType(Class<?> rtype, Class<?>[] ptypes) {
396         return MethodType.makeImpl(rtype, ptypes, true);
397     }
398 
399     /**
400      * The JVM wants to link a call site that requires a dynamic type check.
401      * Name is a type-checking invoker, invokeExact or invoke.
402      * Return a JVM method (MemberName) to handle the invoking.
403      * The method assumes the following arguments on the stack:
404      * 0: the method handle being invoked
405      * 1-N: the arguments to the method handle invocation
406      * N+1: an optional, implicitly added argument (typically the given MethodType)
407      * <p>
408      * The nominal method at such a call site is an instance of
409      * a signature-polymorphic method (see @PolymorphicSignature).
410      * Such method instances are user-visible entities which are
411      * "split" from the generic placeholder method in {@code MethodHandle}.
412      * (Note that the placeholder method is not identical with any of
413      * its instances.  If invoked reflectively, is guaranteed to throw an
414      * {@code UnsupportedOperationException}.)
415      * If the signature-polymorphic method instance is ever reified,
416      * it appears as a "copy" of the original placeholder
417      * (a native final member of {@code MethodHandle}) except
418      * that its type descriptor has shape required by the instance,
419      * and the method instance is <em>not</em> varargs.
420      * The method instance is also marked synthetic, since the
421      * method (by definition) does not appear in Java source code.
422      * <p>
423      * The JVM is allowed to reify this method as instance metadata.
424      * For example, {@code invokeBasic} is always reified.
425      * But the JVM may instead call {@code linkMethod}.
426      * If the result is an * ordered pair of a {@code (method, appendix)},
427      * the method gets all the arguments (0..N inclusive)
428      * plus the appendix (N+1), and uses the appendix to complete the call.
429      * In this way, one reusable method (called a "linker method")
430      * can perform the function of any number of polymorphic instance
431      * methods.
432      * <p>
433      * Linker methods are allowed to be weakly typed, with any or
434      * all references rewritten to {@code Object} and any primitives
435      * (except {@code long}/{@code float}/{@code double})
436      * rewritten to {@code int}.
437      * A linker method is trusted to return a strongly typed result,
438      * according to the specific method type descriptor of the
439      * signature-polymorphic instance it is emulating.
440      * This can involve (as necessary) a dynamic check using
441      * data extracted from the appendix argument.
442      * <p>
443      * The JVM does not inspect the appendix, other than to pass
444      * it verbatim to the linker method at every call.
445      * This means that the JDK runtime has wide latitude
446      * for choosing the shape of each linker method and its
447      * corresponding appendix.
448      * Linker methods should be generated from {@code LambdaForm}s
449      * so that they do not become visible on stack traces.
450      * <p>
451      * The {@code linkMethod} call is free to omit the appendix
452      * (returning null) and instead emulate the required function
453      * completely in the linker method.
454      * As a corner case, if N==255, no appendix is possible.
455      * In this case, the method returned must be custom-generated to
456      * perform any needed type checking.
457      * <p>
458      * If the JVM does not reify a method at a call site, but instead
459      * calls {@code linkMethod}, the corresponding call represented
460      * in the bytecodes may mention a valid method which is not
461      * representable with a {@code MemberName}.
462      * Therefore, use cases for {@code linkMethod} tend to correspond to
463      * special cases in reflective code such as {@code findVirtual}
464      * or {@code revealDirect}.
465      */
466     static MemberName linkMethod(Class<?> callerClass, int refKind,
467                                  Class<?> defc, String name, Object type,
468                                  Object[] appendixResult) {
469         if (!TRACE_METHOD_LINKAGE)
470             return linkMethodImpl(callerClass, refKind, defc, name, type, appendixResult);
471         return linkMethodTracing(callerClass, refKind, defc, name, type, appendixResult);
472     }
473     static MemberName linkMethodImpl(Class<?> callerClass, int refKind,
474                                      Class<?> defc, String name, Object type,
475                                      Object[] appendixResult) {
476         try {
477             if (refKind == REF_invokeVirtual) {
478                 if (defc == MethodHandle.class) {
479                     return Invokers.methodHandleInvokeLinkerMethod(
480                             name, fixMethodType(callerClass, type), appendixResult);
481                 } else if (defc == VarHandle.class) {
482                     return varHandleOperationLinkerMethod(
483                             name, fixMethodType(callerClass, type), appendixResult);
484                 }
485             }
486         } catch (Error e) {
487             // Pass through an Error, including say StackOverflowError or
488             // OutOfMemoryError
489             throw e;
490         } catch (Throwable ex) {
491             // Wrap anything else in LinkageError
492             throw new LinkageError(ex.getMessage(), ex);
493         }
494         throw new LinkageError("no such method "+defc.getName()+"."+name+type);
495     }
496     private static MethodType fixMethodType(Class<?> callerClass, Object type) {
497         if (type instanceof MethodType)
498             return (MethodType) type;
499         else
500             return MethodType.fromDescriptor((String)type, callerClass.getClassLoader());
501     }
502     // Tracing logic:
503     static MemberName linkMethodTracing(Class<?> callerClass, int refKind,
504                                         Class<?> defc, String name, Object type,
505                                         Object[] appendixResult) {
506         System.out.println("linkMethod "+defc.getName()+"."+
507                            name+type+"/"+Integer.toHexString(refKind));
508         try {
509             MemberName res = linkMethodImpl(callerClass, refKind, defc, name, type, appendixResult);
510             System.out.println("linkMethod => "+res+" + "+appendixResult[0]);
511             return res;
512         } catch (Throwable ex) {
513             System.out.println("linkMethod => throw "+ex);
514             throw ex;
515         }
516     }
517 
518     /**
519      * Obtain the method to link to the VarHandle operation.
520      * This method is located here and not in Invokers to avoid
521      * initializing that and other classes early on in VM bootup.
522      */
523     private static MemberName varHandleOperationLinkerMethod(String name,
524                                                              MethodType mtype,
525                                                              Object[] appendixResult) {
526         // Get the signature method type
527         final MethodType sigType = mtype.basicType();
528 
529         // Get the access kind from the method name
530         VarHandle.AccessMode ak;
531         try {
532             ak = VarHandle.AccessMode.valueFromMethodName(name);
533         } catch (IllegalArgumentException e) {
534             throw MethodHandleStatics.newInternalError(e);
535         }
536 
537         // Create the appendix descriptor constant
538         VarHandle.AccessDescriptor ad = new VarHandle.AccessDescriptor(mtype, ak.at.ordinal(), ak.ordinal());
539         appendixResult[0] = ad;
540 
541         if (MethodHandleStatics.VAR_HANDLE_GUARDS) {
542             // If not polymorphic in the return type, such as the compareAndSet
543             // methods that return boolean
544             Class<?> guardReturnType = sigType.returnType();
545             if (ak.at.isMonomorphicInReturnType) {
546                 if (ak.at.returnType != mtype.returnType()) {
547                     // The caller contains a different return type than that
548                     // defined by the method
549                     throw newNoSuchMethodErrorOnVarHandle(name, mtype);
550                 }
551                 // Adjust the return type of the signature method type
552                 guardReturnType = ak.at.returnType;
553             }
554 
555             // Get the guard method type for linking
556             final Class<?>[] guardParams = new Class<?>[sigType.parameterCount() + 2];
557             // VarHandle at start
558             guardParams[0] = VarHandle.class;
559             for (int i = 0; i < sigType.parameterCount(); i++) {
560                 guardParams[i + 1] = sigType.parameterType(i);
561             }
562             // Access descriptor at end
563             guardParams[guardParams.length - 1] = VarHandle.AccessDescriptor.class;
564             MethodType guardType = MethodType.makeImpl(guardReturnType, guardParams, true);
565 
566             MemberName linker = new MemberName(
567                     VarHandleGuards.class, getVarHandleGuardMethodName(guardType),
568                     guardType, REF_invokeStatic);
569 
570             linker = MemberName.getFactory().resolveOrNull(REF_invokeStatic, linker,
571                                                            VarHandleGuards.class, LM_TRUSTED);
572             if (linker != null) {
573                 return linker;
574             }
575             // Fall back to lambda form linkage if guard method is not available
576             // TODO Optionally log fallback ?
577         }
578         return Invokers.varHandleInvokeLinkerMethod(mtype);
579     }
580     static String getVarHandleGuardMethodName(MethodType guardType) {
581         String prefix = "guard_";
582         StringBuilder sb = new StringBuilder(prefix.length() + guardType.parameterCount());
583 
584         sb.append(prefix);
585         for (int i = 1; i < guardType.parameterCount() - 1; i++) {
586             Class<?> pt = guardType.parameterType(i);
587             sb.append(getCharType(pt));
588         }
589         sb.append('_').append(getCharType(guardType.returnType()));
590         return sb.toString();
591     }
592     static char getCharType(Class<?> pt) {
593         return Wrapper.forBasicType(pt).basicTypeChar();
594     }
595     static NoSuchMethodError newNoSuchMethodErrorOnVarHandle(String name, MethodType mtype) {
596         return new NoSuchMethodError("VarHandle." + name + mtype);
597     }
598 
599     /**
600      * The JVM is resolving a CONSTANT_MethodHandle CP entry.  And it wants our help.
601      * It will make an up-call to this method.  (Do not change the name or signature.)
602      * The type argument is a Class for field requests and a MethodType for non-fields.
603      * <p>
604      * Recent versions of the JVM may also pass a resolved MemberName for the type.
605      * In that case, the name is ignored and may be null.
606      */
607     static MethodHandle linkMethodHandleConstant(Class<?> callerClass, int refKind,
608                                                  Class<?> defc, String name, Object type) {
609         try {
610             Lookup lookup = IMPL_LOOKUP.in(callerClass);
611             assert(refKindIsValid(refKind));
612             return lookup.linkMethodHandleConstant((byte) refKind, defc, name, type);
613         } catch (ReflectiveOperationException ex) {
614             throw mapLookupExceptionToError(ex);
615         }
616     }
617 
618     /**
619      * Map a reflective exception to a linkage error.
620      */
621     static LinkageError mapLookupExceptionToError(ReflectiveOperationException ex) {
622         LinkageError err;
623         if (ex instanceof IllegalAccessException) {
624             Throwable cause = ex.getCause();
625             if (cause instanceof AbstractMethodError) {
626                 return (AbstractMethodError) cause;
627             } else {
628                 err = new IllegalAccessError(ex.getMessage());
629             }
630         } else if (ex instanceof NoSuchMethodException) {
631             err = new NoSuchMethodError(ex.getMessage());
632         } else if (ex instanceof NoSuchFieldException) {
633             err = new NoSuchFieldError(ex.getMessage());
634         } else {
635             err = new IncompatibleClassChangeError();
636         }
637         return initCauseFrom(err, ex);
638     }
639 
640     /**
641      * Use best possible cause for err.initCause(), substituting the
642      * cause for err itself if the cause has the same (or better) type.
643      */
644     static <E extends Error> E initCauseFrom(E err, Exception ex) {
645         Throwable th = ex.getCause();
646         @SuppressWarnings("unchecked")
647         final Class<E> Eclass = (Class<E>) err.getClass();
648         if (Eclass.isInstance(th))
649            return Eclass.cast(th);
650         err.initCause(th == null ? ex : th);
651         return err;
652     }
653 
654     /**
655      * Is this method a caller-sensitive method?
656      * I.e., does it call Reflection.getCallerClass or a similar method
657      * to ask about the identity of its caller?
658      */
659     static boolean isCallerSensitive(MemberName mem) {
660         if (!mem.isInvocable())  return false;  // fields are not caller sensitive
661 
662         return mem.isCallerSensitive() || canBeCalledVirtual(mem);
663     }
664 
665     static boolean canBeCalledVirtual(MemberName mem) {
666         assert(mem.isInvocable());
667         return mem.getName().equals("getContextClassLoader") && canBeCalledVirtual(mem, java.lang.Thread.class);
668     }
669 
670     static boolean canBeCalledVirtual(MemberName symbolicRef, Class<?> definingClass) {
671         Class<?> symbolicRefClass = symbolicRef.getDeclaringClass();
672         if (symbolicRefClass == definingClass)  return true;
673         if (symbolicRef.isStatic() || symbolicRef.isPrivate())  return false;
674         return (definingClass.isAssignableFrom(symbolicRefClass) ||  // Msym overrides Mdef
675                 symbolicRefClass.isInterface());                     // Mdef implements Msym
676     }
677 }
--- EOF ---