1 /*
   2  * Copyright (c) 2015, 2019, 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.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "code/compiledIC.hpp"
  27 #include "code/compiledMethod.inline.hpp"
  28 #include "code/exceptionHandlerTable.hpp"
  29 #include "code/scopeDesc.hpp"
  30 #include "code/codeCache.hpp"
  31 #include "code/icBuffer.hpp"
  32 #include "gc/shared/barrierSet.hpp"
  33 #include "gc/shared/gcBehaviours.hpp"
  34 #include "interpreter/bytecode.inline.hpp"
  35 #include "logging/log.hpp"
  36 #include "logging/logTag.hpp"
  37 #include "memory/resourceArea.hpp"
  38 #include "oops/methodData.hpp"
  39 #include "oops/method.inline.hpp"
  40 #include "prims/methodHandles.hpp"
  41 #include "runtime/deoptimization.hpp"
  42 #include "runtime/handles.inline.hpp"
  43 #include "runtime/mutexLocker.hpp"
  44 #include "runtime/sharedRuntime.hpp"
  45 
  46 CompiledMethod::CompiledMethod(Method* method, const char* name, CompilerType type, const CodeBlobLayout& layout,
  47                                int frame_complete_offset, int frame_size, ImmutableOopMapSet* oop_maps,
  48                                bool caller_must_gc_arguments)
  49   : CodeBlob(name, type, layout, frame_complete_offset, frame_size, oop_maps, caller_must_gc_arguments),
  50     _mark_for_deoptimization_status(not_marked),
  51     _method(method),
  52     _gc_data(NULL)
  53 {
  54   init_defaults();
  55 }
  56 
  57 CompiledMethod::CompiledMethod(Method* method, const char* name, CompilerType type, int size,
  58                                int header_size, CodeBuffer* cb, int frame_complete_offset, int frame_size,
  59                                OopMapSet* oop_maps, bool caller_must_gc_arguments)
  60   : CodeBlob(name, type, CodeBlobLayout((address) this, size, header_size, cb), cb,
  61              frame_complete_offset, frame_size, oop_maps, caller_must_gc_arguments),
  62     _mark_for_deoptimization_status(not_marked),
  63     _method(method),
  64     _gc_data(NULL)
  65 {
  66   init_defaults();
  67 }
  68 
  69 void CompiledMethod::init_defaults() {
  70   _has_unsafe_access          = 0;
  71   _has_method_handle_invokes  = 0;
  72   _lazy_critical_native       = 0;
  73   _has_wide_vectors           = 0;
  74 }
  75 
  76 bool CompiledMethod::is_method_handle_return(address return_pc) {
  77   if (!has_method_handle_invokes())  return false;
  78   PcDesc* pd = pc_desc_at(return_pc);
  79   if (pd == NULL)
  80     return false;
  81   return pd->is_method_handle_invoke();
  82 }
  83 
  84 // Returns a string version of the method state.
  85 const char* CompiledMethod::state() const {
  86   int state = get_state();
  87   switch (state) {
  88   case not_installed:
  89     return "not installed";
  90   case in_use:
  91     return "in use";
  92   case not_used:
  93     return "not_used";
  94   case not_entrant:
  95     return "not_entrant";
  96   case zombie:
  97     return "zombie";
  98   case unloaded:
  99     return "unloaded";
 100   default:
 101     fatal("unexpected method state: %d", state);
 102     return NULL;
 103   }
 104 }
 105 
 106 //-----------------------------------------------------------------------------
 107 
 108 ExceptionCache* CompiledMethod::exception_cache_acquire() const {
 109   return OrderAccess::load_acquire(&_exception_cache);
 110 }
 111 
 112 void CompiledMethod::add_exception_cache_entry(ExceptionCache* new_entry) {
 113   assert(ExceptionCache_lock->owned_by_self(),"Must hold the ExceptionCache_lock");
 114   assert(new_entry != NULL,"Must be non null");
 115   assert(new_entry->next() == NULL, "Must be null");
 116 
 117   for (;;) {
 118     ExceptionCache *ec = exception_cache();
 119     if (ec != NULL) {
 120       Klass* ex_klass = ec->exception_type();
 121       if (!ex_klass->is_loader_alive()) {
 122         // We must guarantee that entries are not inserted with new next pointer
 123         // edges to ExceptionCache entries with dead klasses, due to bad interactions
 124         // with concurrent ExceptionCache cleanup. Therefore, the inserts roll
 125         // the head pointer forward to the first live ExceptionCache, so that the new
 126         // next pointers always point at live ExceptionCaches, that are not removed due
 127         // to concurrent ExceptionCache cleanup.
 128         ExceptionCache* next = ec->next();
 129         if (Atomic::cmpxchg(next, &_exception_cache, ec) == ec) {
 130           CodeCache::release_exception_cache(ec);
 131         }
 132         continue;
 133       }
 134       ec = exception_cache();
 135       if (ec != NULL) {
 136         new_entry->set_next(ec);
 137       }
 138     }
 139     if (Atomic::cmpxchg(new_entry, &_exception_cache, ec) == ec) {
 140       return;
 141     }
 142   }
 143 }
 144 
 145 void CompiledMethod::clean_exception_cache() {
 146   // For each nmethod, only a single thread may call this cleanup function
 147   // at the same time, whether called in STW cleanup or concurrent cleanup.
 148   // Note that if the GC is processing exception cache cleaning in a concurrent phase,
 149   // then a single writer may contend with cleaning up the head pointer to the
 150   // first ExceptionCache node that has a Klass* that is alive. That is fine,
 151   // as long as there is no concurrent cleanup of next pointers from concurrent writers.
 152   // And the concurrent writers do not clean up next pointers, only the head.
 153   // Also note that concurent readers will walk through Klass* pointers that are not
 154   // alive. That does not cause ABA problems, because Klass* is deleted after
 155   // a handshake with all threads, after all stale ExceptionCaches have been
 156   // unlinked. That is also when the CodeCache::exception_cache_purge_list()
 157   // is deleted, with all ExceptionCache entries that were cleaned concurrently.
 158   // That similarly implies that CAS operations on ExceptionCache entries do not
 159   // suffer from ABA problems as unlinking and deletion is separated by a global
 160   // handshake operation.
 161   ExceptionCache* prev = NULL;
 162   ExceptionCache* curr = exception_cache_acquire();
 163 
 164   while (curr != NULL) {
 165     ExceptionCache* next = curr->next();
 166 
 167     if (!curr->exception_type()->is_loader_alive()) {
 168       if (prev == NULL) {
 169         // Try to clean head; this is contended by concurrent inserts, that
 170         // both lazily clean the head, and insert entries at the head. If
 171         // the CAS fails, the operation is restarted.
 172         if (Atomic::cmpxchg(next, &_exception_cache, curr) != curr) {
 173           prev = NULL;
 174           curr = exception_cache_acquire();
 175           continue;
 176         }
 177       } else {
 178         // It is impossible to during cleanup connect the next pointer to
 179         // an ExceptionCache that has not been published before a safepoint
 180         // prior to the cleanup. Therefore, release is not required.
 181         prev->set_next(next);
 182       }
 183       // prev stays the same.
 184 
 185       CodeCache::release_exception_cache(curr);
 186     } else {
 187       prev = curr;
 188     }
 189 
 190     curr = next;
 191   }
 192 }
 193 
 194 // public method for accessing the exception cache
 195 // These are the public access methods.
 196 address CompiledMethod::handler_for_exception_and_pc(Handle exception, address pc) {
 197   // We never grab a lock to read the exception cache, so we may
 198   // have false negatives. This is okay, as it can only happen during
 199   // the first few exception lookups for a given nmethod.
 200   ExceptionCache* ec = exception_cache_acquire();
 201   while (ec != NULL) {
 202     address ret_val;
 203     if ((ret_val = ec->match(exception,pc)) != NULL) {
 204       return ret_val;
 205     }
 206     ec = ec->next();
 207   }
 208   return NULL;
 209 }
 210 
 211 void CompiledMethod::add_handler_for_exception_and_pc(Handle exception, address pc, address handler) {
 212   // There are potential race conditions during exception cache updates, so we
 213   // must own the ExceptionCache_lock before doing ANY modifications. Because
 214   // we don't lock during reads, it is possible to have several threads attempt
 215   // to update the cache with the same data. We need to check for already inserted
 216   // copies of the current data before adding it.
 217 
 218   MutexLocker ml(ExceptionCache_lock);
 219   ExceptionCache* target_entry = exception_cache_entry_for_exception(exception);
 220 
 221   if (target_entry == NULL || !target_entry->add_address_and_handler(pc,handler)) {
 222     target_entry = new ExceptionCache(exception,pc,handler);
 223     add_exception_cache_entry(target_entry);
 224   }
 225 }
 226 
 227 // private method for handling exception cache
 228 // These methods are private, and used to manipulate the exception cache
 229 // directly.
 230 ExceptionCache* CompiledMethod::exception_cache_entry_for_exception(Handle exception) {
 231   ExceptionCache* ec = exception_cache_acquire();
 232   while (ec != NULL) {
 233     if (ec->match_exception_with_space(exception)) {
 234       return ec;
 235     }
 236     ec = ec->next();
 237   }
 238   return NULL;
 239 }
 240 
 241 //-------------end of code for ExceptionCache--------------
 242 
 243 bool CompiledMethod::is_at_poll_return(address pc) {
 244   RelocIterator iter(this, pc, pc+1);
 245   while (iter.next()) {
 246     if (iter.type() == relocInfo::poll_return_type)
 247       return true;
 248   }
 249   return false;
 250 }
 251 
 252 
 253 bool CompiledMethod::is_at_poll_or_poll_return(address pc) {
 254   RelocIterator iter(this, pc, pc+1);
 255   while (iter.next()) {
 256     relocInfo::relocType t = iter.type();
 257     if (t == relocInfo::poll_return_type || t == relocInfo::poll_type)
 258       return true;
 259   }
 260   return false;
 261 }
 262 
 263 void CompiledMethod::verify_oop_relocations() {
 264   // Ensure sure that the code matches the current oop values
 265   RelocIterator iter(this, NULL, NULL);
 266   while (iter.next()) {
 267     if (iter.type() == relocInfo::oop_type) {
 268       oop_Relocation* reloc = iter.oop_reloc();
 269       if (!reloc->oop_is_immediate()) {
 270         reloc->verify_oop_relocation();
 271       }
 272     }
 273   }
 274 }
 275 
 276 
 277 ScopeDesc* CompiledMethod::scope_desc_at(address pc) {
 278   PcDesc* pd = pc_desc_at(pc);
 279   guarantee(pd != NULL, "scope must be present");
 280   return new ScopeDesc(this, pd->scope_decode_offset(),
 281                        pd->obj_decode_offset(), pd->should_reexecute(), pd->rethrow_exception(),
 282                        pd->return_oop());
 283 }
 284 
 285 ScopeDesc* CompiledMethod::scope_desc_near(address pc) {
 286   PcDesc* pd = pc_desc_near(pc);
 287   guarantee(pd != NULL, "scope must be present");
 288   return new ScopeDesc(this, pd->scope_decode_offset(),
 289                        pd->obj_decode_offset(), pd->should_reexecute(), pd->rethrow_exception(),
 290                        pd->return_oop());
 291 }
 292 
 293 address CompiledMethod::oops_reloc_begin() const {
 294   // If the method is not entrant or zombie then a JMP is plastered over the
 295   // first few bytes.  If an oop in the old code was there, that oop
 296   // should not get GC'd.  Skip the first few bytes of oops on
 297   // not-entrant methods.
 298   if (frame_complete_offset() != CodeOffsets::frame_never_safe &&
 299       code_begin() + frame_complete_offset() >
 300       verified_entry_point() + NativeJump::instruction_size)
 301   {
 302     // If we have a frame_complete_offset after the native jump, then there
 303     // is no point trying to look for oops before that. This is a requirement
 304     // for being allowed to scan oops concurrently.
 305     return code_begin() + frame_complete_offset();
 306   }
 307 
 308   // It is not safe to read oops concurrently using entry barriers, if their
 309   // location depend on whether the nmethod is entrant or not.
 310   assert(BarrierSet::barrier_set()->barrier_set_nmethod() == NULL, "Not safe oop scan");
 311 
 312   address low_boundary = verified_entry_point();
 313   if (!is_in_use() && is_nmethod()) {
 314     low_boundary += NativeJump::instruction_size;
 315     // %%% Note:  On SPARC we patch only a 4-byte trap, not a full NativeJump.
 316     // This means that the low_boundary is going to be a little too high.
 317     // This shouldn't matter, since oops of non-entrant methods are never used.
 318     // In fact, why are we bothering to look at oops in a non-entrant method??
 319   }
 320   return low_boundary;
 321 }
 322 
 323 int CompiledMethod::verify_icholder_relocations() {
 324   ResourceMark rm;
 325   int count = 0;
 326 
 327   RelocIterator iter(this);
 328   while(iter.next()) {
 329     if (iter.type() == relocInfo::virtual_call_type) {
 330       if (CompiledIC::is_icholder_call_site(iter.virtual_call_reloc(), this)) {
 331         CompiledIC *ic = CompiledIC_at(&iter);
 332         if (TraceCompiledIC) {
 333           tty->print("noticed icholder " INTPTR_FORMAT " ", p2i(ic->cached_icholder()));
 334           ic->print();
 335         }
 336         assert(ic->cached_icholder() != NULL, "must be non-NULL");
 337         count++;
 338       }
 339     }
 340   }
 341 
 342   return count;
 343 }
 344 
 345 // Method that knows how to preserve outgoing arguments at call. This method must be
 346 // called with a frame corresponding to a Java invoke
 347 void CompiledMethod::preserve_callee_argument_oops(frame fr, const RegisterMap *reg_map, OopClosure* f) {
 348   if (method() != NULL && !method()->is_native()) {
 349     address pc = fr.pc();
 350     SimpleScopeDesc ssd(this, pc);
 351     Bytecode_invoke call(ssd.method(), ssd.bci());
 352     bool has_receiver = call.has_receiver();
 353     bool has_appendix = call.has_appendix();
 354     Symbol* signature = call.signature();
 355 
 356     // The method attached by JIT-compilers should be used, if present.
 357     // Bytecode can be inaccurate in such case.
 358     Method* callee = attached_method_before_pc(pc);
 359     if (callee != NULL) {
 360       has_receiver = !(callee->access_flags().is_static());
 361       has_appendix = false;
 362       signature = callee->signature();
 363     }
 364 
 365     fr.oops_compiled_arguments_do(signature, has_receiver, has_appendix, reg_map, f);
 366   }
 367 }
 368 
 369 Method* CompiledMethod::attached_method(address call_instr) {
 370   assert(code_contains(call_instr), "not part of the nmethod");
 371   RelocIterator iter(this, call_instr, call_instr + 1);
 372   while (iter.next()) {
 373     if (iter.addr() == call_instr) {
 374       switch(iter.type()) {
 375         case relocInfo::static_call_type:      return iter.static_call_reloc()->method_value();
 376         case relocInfo::opt_virtual_call_type: return iter.opt_virtual_call_reloc()->method_value();
 377         case relocInfo::virtual_call_type:     return iter.virtual_call_reloc()->method_value();
 378         default:                               break;
 379       }
 380     }
 381   }
 382   return NULL; // not found
 383 }
 384 
 385 Method* CompiledMethod::attached_method_before_pc(address pc) {
 386   if (NativeCall::is_call_before(pc)) {
 387     NativeCall* ncall = nativeCall_before(pc);
 388     return attached_method(ncall->instruction_address());
 389   }
 390   return NULL; // not a call
 391 }
 392 
 393 void CompiledMethod::clear_inline_caches() {
 394   assert(SafepointSynchronize::is_at_safepoint(), "cleaning of IC's only allowed at safepoint");
 395   if (is_zombie()) {
 396     return;
 397   }
 398 
 399   RelocIterator iter(this);
 400   while (iter.next()) {
 401     iter.reloc()->clear_inline_cache();
 402   }
 403 }
 404 
 405 // Clear IC callsites, releasing ICStubs of all compiled ICs
 406 // as well as any associated CompiledICHolders.
 407 void CompiledMethod::clear_ic_callsites() {
 408   assert(CompiledICLocker::is_safe(this), "mt unsafe call");
 409   ResourceMark rm;
 410   RelocIterator iter(this);
 411   while(iter.next()) {
 412     if (iter.type() == relocInfo::virtual_call_type) {
 413       CompiledIC* ic = CompiledIC_at(&iter);
 414       ic->set_to_clean(false);
 415     }
 416   }
 417 }
 418 
 419 #ifdef ASSERT
 420 // Check class_loader is alive for this bit of metadata.
 421 class CheckClass : public MetadataClosure {
 422   void do_metadata(Metadata* md) {
 423     Klass* klass = NULL;
 424     if (md->is_klass()) {
 425       klass = ((Klass*)md);
 426     } else if (md->is_method()) {
 427       klass = ((Method*)md)->method_holder();
 428     } else if (md->is_methodData()) {
 429       klass = ((MethodData*)md)->method()->method_holder();
 430     } else {
 431       md->print();
 432       ShouldNotReachHere();
 433     }
 434     assert(klass->is_loader_alive(), "must be alive");
 435   }
 436 };
 437 #endif // ASSERT
 438 
 439 
 440 bool CompiledMethod::clean_ic_if_metadata_is_dead(CompiledIC *ic) {
 441   if (ic->is_clean()) {
 442     return true;
 443   }
 444   if (ic->is_icholder_call()) {
 445     // The only exception is compiledICHolder metdata which may
 446     // yet be marked below. (We check this further below).
 447     CompiledICHolder* cichk_metdata = ic->cached_icholder();
 448 
 449     if (cichk_metdata->is_loader_alive()) {
 450       return true;
 451     }
 452   } else {
 453     Metadata* ic_metdata = ic->cached_metadata();
 454     if (ic_metdata != NULL) {
 455       if (ic_metdata->is_klass()) {
 456         if (((Klass*)ic_metdata)->is_loader_alive()) {
 457           return true;
 458         }
 459       } else if (ic_metdata->is_method()) {
 460         Method* method = (Method*)ic_metdata;
 461         assert(!method->is_old(), "old method should have been cleaned");
 462         if (method->method_holder()->is_loader_alive()) {
 463           return true;
 464         }
 465       } else {
 466         ShouldNotReachHere();
 467       }
 468     }
 469   }
 470 
 471   return ic->set_to_clean();
 472 }
 473 
 474 // Clean references to unloaded nmethods at addr from this one, which is not unloaded.
 475 template <class CompiledICorStaticCall>
 476 static bool clean_if_nmethod_is_unloaded(CompiledICorStaticCall *ic, address addr, CompiledMethod* from,
 477                                          bool clean_all) {
 478   // Ok, to lookup references to zombies here
 479   CodeBlob *cb = CodeCache::find_blob_unsafe(addr);
 480   CompiledMethod* nm = (cb != NULL) ? cb->as_compiled_method_or_null() : NULL;
 481   if (nm != NULL) {
 482     // Clean inline caches pointing to both zombie and not_entrant methods
 483     if (clean_all || !nm->is_in_use() || nm->is_unloading() || (nm->method()->code() != nm)) {
 484       if (!ic->set_to_clean(from->is_alive())) {
 485         return false;
 486       }
 487       assert(ic->is_clean(), "nmethod " PTR_FORMAT "not clean %s", p2i(from), from->method()->name_and_sig_as_C_string());
 488     }
 489   }
 490   return true;
 491 }
 492 
 493 static bool clean_if_nmethod_is_unloaded(CompiledIC *ic, CompiledMethod* from,
 494                                          bool clean_all) {
 495   return clean_if_nmethod_is_unloaded(ic, ic->ic_destination(), from, clean_all);
 496 }
 497 
 498 static bool clean_if_nmethod_is_unloaded(CompiledStaticCall *csc, CompiledMethod* from,
 499                                          bool clean_all) {
 500   return clean_if_nmethod_is_unloaded(csc, csc->destination(), from, clean_all);
 501 }
 502 
 503 // Cleans caches in nmethods that point to either classes that are unloaded
 504 // or nmethods that are unloaded.
 505 //
 506 // Can be called either in parallel by G1 currently or after all
 507 // nmethods are unloaded.  Return postponed=true in the parallel case for
 508 // inline caches found that point to nmethods that are not yet visited during
 509 // the do_unloading walk.
 510 bool CompiledMethod::unload_nmethod_caches(bool unloading_occurred) {
 511   ResourceMark rm;
 512 
 513   // Exception cache only needs to be called if unloading occurred
 514   if (unloading_occurred) {
 515     clean_exception_cache();
 516   }
 517 
 518   if (!cleanup_inline_caches_impl(unloading_occurred, false)) {
 519     return false;
 520   }
 521 
 522 #ifdef ASSERT
 523   // Check that the metadata embedded in the nmethod is alive
 524   CheckClass check_class;
 525   metadata_do(&check_class);
 526 #endif
 527   return true;
 528 }
 529 
 530 void CompiledMethod::cleanup_inline_caches(bool clean_all) {
 531   for (;;) {
 532     ICRefillVerifier ic_refill_verifier;
 533     { CompiledICLocker ic_locker(this);
 534       if (cleanup_inline_caches_impl(false, clean_all)) {
 535         return;
 536       }
 537     }
 538     InlineCacheBuffer::refill_ic_stubs();
 539   }
 540 }
 541 
 542 // Called to clean up after class unloading for live nmethods and from the sweeper
 543 // for all methods.
 544 bool CompiledMethod::cleanup_inline_caches_impl(bool unloading_occurred, bool clean_all) {
 545   assert(CompiledICLocker::is_safe(this), "mt unsafe call");
 546   ResourceMark rm;
 547 
 548   // Find all calls in an nmethod and clear the ones that point to non-entrant,
 549   // zombie and unloaded nmethods.
 550   RelocIterator iter(this, oops_reloc_begin());
 551   bool is_in_static_stub = false;
 552   while(iter.next()) {
 553 
 554     switch (iter.type()) {
 555 
 556     case relocInfo::virtual_call_type:
 557       if (unloading_occurred) {
 558         // If class unloading occurred we first clear ICs where the cached metadata
 559         // is referring to an unloaded klass or method.
 560         if (!clean_ic_if_metadata_is_dead(CompiledIC_at(&iter))) {
 561           return false;
 562         }
 563       }
 564 
 565       if (!clean_if_nmethod_is_unloaded(CompiledIC_at(&iter), this, clean_all)) {
 566         return false;
 567       }
 568       break;
 569 
 570     case relocInfo::opt_virtual_call_type:
 571       if (!clean_if_nmethod_is_unloaded(CompiledIC_at(&iter), this, clean_all)) {
 572         return false;
 573       }
 574       break;
 575 
 576     case relocInfo::static_call_type:
 577       if (!clean_if_nmethod_is_unloaded(compiledStaticCall_at(iter.reloc()), this, clean_all)) {
 578         return false;
 579       }
 580       break;
 581 
 582     case relocInfo::static_stub_type: {
 583       is_in_static_stub = true;
 584       break;
 585     }
 586 
 587     case relocInfo::metadata_type: {
 588       // Only the metadata relocations contained in static/opt virtual call stubs
 589       // contains the Method* passed to c2i adapters. It is the only metadata
 590       // relocation that needs to be walked, as it is the one metadata relocation
 591       // that violates the invariant that all metadata relocations have an oop
 592       // in the compiled method (due to deferred resolution and code patching).
 593 
 594       // This causes dead metadata to remain in compiled methods that are not
 595       // unloading. Unless these slippery metadata relocations of the static
 596       // stubs are at least cleared, subsequent class redefinition operations
 597       // will access potentially free memory, and JavaThread execution
 598       // concurrent to class unloading may call c2i adapters with dead methods.
 599       if (!is_in_static_stub) {
 600         // The first metadata relocation after a static stub relocation is the
 601         // metadata relocation of the static stub used to pass the Method* to
 602         // c2i adapters.
 603         continue;
 604       }
 605       is_in_static_stub = false;
 606       metadata_Relocation* r = iter.metadata_reloc();
 607       Metadata* md = r->metadata_value();
 608       if (md != NULL && md->is_method()) {
 609         Method* method = static_cast<Method*>(md);
 610         if (!method->method_holder()->is_loader_alive()) {
 611           Atomic::store((Method*)NULL, r->metadata_addr());
 612 
 613           if (!r->metadata_is_immediate()) {
 614             r->fix_metadata_relocation();
 615           }
 616         }
 617       }
 618       break;
 619     }
 620 
 621     default:
 622       break;
 623     }
 624   }
 625 
 626   return true;
 627 }
 628 
 629 // Iterating over all nmethods, e.g. with the help of CodeCache::nmethods_do(fun) was found
 630 // to not be inherently safe. There is a chance that fields are seen which are not properly
 631 // initialized. This happens despite the fact that nmethods_do() asserts the CodeCache_lock
 632 // to be held.
 633 // To bundle knowledge about necessary checks in one place, this function was introduced.
 634 // It is not claimed that these checks are sufficient, but they were found to be necessary.
 635 bool CompiledMethod::nmethod_access_is_safe(nmethod* nm) {
 636   Method* method = (nm == NULL) ? NULL : nm->method();  // nm->method() may be uninitialized, i.e. != NULL, but invalid
 637   return (nm != NULL) && (method != NULL) && (method->signature() != NULL) &&
 638          !nm->is_zombie() && !nm->is_not_installed() &&
 639          os::is_readable_pointer(method) &&
 640          os::is_readable_pointer(method->constants()) &&
 641          os::is_readable_pointer(method->signature());
 642 }
 643 
 644 address CompiledMethod::continuation_for_implicit_exception(address pc, bool for_div0_check) {
 645   // Exception happened outside inline-cache check code => we are inside
 646   // an active nmethod => use cpc to determine a return address
 647   int exception_offset = pc - code_begin();
 648   int cont_offset = ImplicitExceptionTable(this).continuation_offset( exception_offset );
 649 #ifdef ASSERT
 650   if (cont_offset == 0) {
 651     Thread* thread = Thread::current();
 652     ResetNoHandleMark rnm; // Might be called from LEAF/QUICK ENTRY
 653     HandleMark hm(thread);
 654     ResourceMark rm(thread);
 655     CodeBlob* cb = CodeCache::find_blob(pc);
 656     assert(cb != NULL && cb == this, "");
 657     ttyLocker ttyl;
 658     tty->print_cr("implicit exception happened at " INTPTR_FORMAT, p2i(pc));
 659     print();
 660     method()->print_codes();
 661     print_code();
 662     print_pcs();
 663   }
 664 #endif
 665   if (cont_offset == 0) {
 666     // Let the normal error handling report the exception
 667     return NULL;
 668   }
 669   if (cont_offset == exception_offset) {
 670 #if INCLUDE_JVMCI
 671     Deoptimization::DeoptReason deopt_reason = for_div0_check ? Deoptimization::Reason_div0_check : Deoptimization::Reason_null_check;
 672     JavaThread *thread = JavaThread::current();
 673     thread->set_jvmci_implicit_exception_pc(pc);
 674     thread->set_pending_deoptimization(Deoptimization::make_trap_request(deopt_reason,
 675                                                                          Deoptimization::Action_reinterpret));
 676     return (SharedRuntime::deopt_blob()->implicit_exception_uncommon_trap());
 677 #else
 678     ShouldNotReachHere();
 679 #endif
 680   }
 681   return code_begin() + cont_offset;
 682 }
 683 
 684 class HasEvolDependency : public MetadataClosure {
 685   bool _has_evol_dependency;
 686  public:
 687   HasEvolDependency() : _has_evol_dependency(false) {}
 688   void do_metadata(Metadata* md) {
 689     if (md->is_method()) {
 690       Method* method = (Method*)md;
 691       if (method->is_old()) {
 692         _has_evol_dependency = true;
 693       }
 694     }
 695   }
 696   bool has_evol_dependency() const { return _has_evol_dependency; }
 697 };
 698 
 699 bool CompiledMethod::has_evol_metadata() {
 700   // Check the metadata in relocIter and CompiledIC and also deoptimize
 701   // any nmethod that has reference to old methods.
 702   HasEvolDependency check_evol;
 703   metadata_do(&check_evol);
 704   if (check_evol.has_evol_dependency() && log_is_enabled(Debug, redefine, class, nmethod)) {
 705     ResourceMark rm;
 706     log_debug(redefine, class, nmethod)
 707             ("Found evol dependency of nmethod %s.%s(%s) compile_id=%d on in nmethod metadata",
 708              _method->method_holder()->external_name(),
 709              _method->name()->as_C_string(),
 710              _method->signature()->as_C_string(),
 711              compile_id());
 712   }
 713   return check_evol.has_evol_dependency();
 714 }