1 /*
   2  * Copyright (c) 2018, 2025, 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 "classfile/javaClasses.inline.hpp"
  26 #include "classfile/vmSymbols.hpp"
  27 #include "code/codeCache.inline.hpp"
  28 #include "code/nmethod.inline.hpp"
  29 #include "code/vmreg.inline.hpp"
  30 #include "compiler/oopMap.inline.hpp"
  31 #include "gc/shared/barrierSet.hpp"
  32 #include "gc/shared/continuationGCSupport.inline.hpp"
  33 #include "gc/shared/gc_globals.hpp"
  34 #include "gc/shared/memAllocator.hpp"
  35 #include "gc/shared/threadLocalAllocBuffer.inline.hpp"
  36 #include "interpreter/interpreter.hpp"
  37 #include "jfr/jfrEvents.hpp"
  38 #include "logging/log.hpp"
  39 #include "logging/logStream.hpp"
  40 #include "oops/access.inline.hpp"
  41 #include "oops/method.inline.hpp"
  42 #include "oops/objArrayOop.inline.hpp"
  43 #include "oops/oopsHierarchy.hpp"
  44 #include "oops/stackChunkOop.inline.hpp"
  45 #include "prims/jvmtiThreadState.hpp"
  46 #include "runtime/arguments.hpp"
  47 #include "runtime/continuation.hpp"
  48 #include "runtime/continuationEntry.inline.hpp"
  49 #include "runtime/continuationHelper.inline.hpp"
  50 #include "runtime/continuationJavaClasses.inline.hpp"
  51 #include "runtime/continuationWrapper.inline.hpp"
  52 #include "runtime/frame.inline.hpp"
  53 #include "runtime/interfaceSupport.inline.hpp"
  54 #include "runtime/javaThread.inline.hpp"
  55 #include "runtime/jniHandles.inline.hpp"
  56 #include "runtime/keepStackGCProcessed.hpp"
  57 #include "runtime/objectMonitor.inline.hpp"
  58 #include "runtime/orderAccess.hpp"
  59 #include "runtime/prefetch.inline.hpp"
  60 #include "runtime/sharedRuntime.hpp"
  61 #include "runtime/smallRegisterMap.inline.hpp"
  62 #include "runtime/stackChunkFrameStream.inline.hpp"
  63 #include "runtime/stackFrameStream.inline.hpp"
  64 #include "runtime/stackOverflow.hpp"
  65 #include "runtime/stackWatermarkSet.inline.hpp"
  66 #include "utilities/debug.hpp"
  67 #include "utilities/exceptions.hpp"
  68 #include "utilities/macros.hpp"
  69 #include "utilities/vmError.hpp"
  70 #if INCLUDE_ZGC
  71 #include "gc/z/zStackChunkGCData.inline.hpp"
  72 #endif
  73 #if INCLUDE_JFR
  74 #include "jfr/jfr.inline.hpp"
  75 #endif
  76 
  77 #include <type_traits>
  78 
  79 /*
  80  * This file contains the implementation of continuation freezing (yield) and thawing (run).
  81  *
  82  * This code is very latency-critical and very hot. An ordinary and well-behaved server application
  83  * would likely call these operations many thousands of times per second second, on every core.
  84  *
  85  * Freeze might be called every time the application performs any I/O operation, every time it
  86  * acquires a j.u.c. lock, every time it takes a message from a queue, and thaw can be called
  87  * multiple times in each of those cases, as it is called by the return barrier, which may be
  88  * invoked on method return.
  89  *
  90  * The amortized budget for each of those two operations is ~100-150ns. That is why, for
  91  * example, every effort is made to avoid Java-VM transitions as much as possible.
  92  *
  93  * On the fast path, all frames are known to be compiled, and the chunk requires no barriers
  94  * and so frames simply copied, and the bottom-most one is patched.
  95  * On the slow path, internal pointers in interpreted frames are de/relativized to/from offsets
  96  * and absolute pointers, and barriers invoked.
  97  */
  98 
  99 /************************************************
 100 
 101 Thread-stack layout on freeze/thaw.
 102 See corresponding stack-chunk layout in instanceStackChunkKlass.hpp
 103 
 104             +----------------------------+
 105             |      .                     |
 106             |      .                     |
 107             |      .                     |
 108             |   carrier frames           |
 109             |                            |
 110             |----------------------------|
 111             |                            |
 112             |    Continuation.run        |
 113             |                            |
 114             |============================|
 115             |    enterSpecial frame      |
 116             |  pc                        |
 117             |  rbp                       |
 118             |  -----                     |
 119         ^   |  int argsize               | = ContinuationEntry
 120         |   |  oopDesc* cont             |
 121         |   |  oopDesc* chunk            |
 122         |   |  ContinuationEntry* parent |
 123         |   |  ...                       |
 124         |   |============================| <------ JavaThread::_cont_entry = entry->sp()
 125         |   |  ? alignment word ?        |
 126         |   |----------------------------| <--\
 127         |   |                            |    |
 128         |   |  ? caller stack args ?     |    |   argsize (might not be 2-word aligned) words
 129 Address |   |                            |    |   Caller is still in the chunk.
 130         |   |----------------------------|    |
 131         |   |  pc (? return barrier ?)   |    |  This pc contains the return barrier when the bottom-most frame
 132         |   |  rbp                       |    |  isn't the last one in the continuation.
 133         |   |                            |    |
 134         |   |    frame                   |    |
 135         |   |                            |    |
 136             +----------------------------|     \__ Continuation frames to be frozen/thawed
 137             |                            |     /
 138             |    frame                   |    |
 139             |                            |    |
 140             |----------------------------|    |
 141             |                            |    |
 142             |    frame                   |    |
 143             |                            |    |
 144             |----------------------------| <--/
 145             |                            |
 146             |    doYield/safepoint stub  | When preempting forcefully, we could have a safepoint stub
 147             |                            | instead of a doYield stub
 148             |============================| <- the sp passed to freeze
 149             |                            |
 150             |  Native freeze/thaw frames |
 151             |      .                     |
 152             |      .                     |
 153             |      .                     |
 154             +----------------------------+
 155 
 156 ************************************************/
 157 
 158 static const bool TEST_THAW_ONE_CHUNK_FRAME = false; // force thawing frames one-at-a-time for testing
 159 
 160 #define CONT_JFR false // emit low-level JFR events that count slow/fast path for continuation performance debugging only
 161 #if CONT_JFR
 162   #define CONT_JFR_ONLY(code) code
 163 #else
 164   #define CONT_JFR_ONLY(code)
 165 #endif
 166 
 167 // TODO: See AbstractAssembler::generate_stack_overflow_check,
 168 // Compile::bang_size_in_bytes(), m->as_SafePoint()->jvms()->interpreter_frame_size()
 169 // when we stack-bang, we need to update a thread field with the lowest (farthest) bang point.
 170 
 171 // Data invariants are defined by Continuation::debug_verify_continuation and Continuation::debug_verify_stack_chunk
 172 
 173 // Used to just annotatate cold/hot branches
 174 #define LIKELY(condition)   (condition)
 175 #define UNLIKELY(condition) (condition)
 176 
 177 // debugging functions
 178 #ifdef ASSERT
 179 extern "C" bool dbg_is_safe(const void* p, intptr_t errvalue); // address p is readable and *(intptr_t*)p != errvalue
 180 
 181 static void verify_continuation(oop continuation) { Continuation::debug_verify_continuation(continuation); }
 182 
 183 static void do_deopt_after_thaw(JavaThread* thread);
 184 static bool do_verify_after_thaw(JavaThread* thread, stackChunkOop chunk, outputStream* st);
 185 static void log_frames(JavaThread* thread);
 186 static void log_frames_after_thaw(JavaThread* thread, ContinuationWrapper& cont, intptr_t* sp, bool preempted);
 187 static void print_frame_layout(const frame& f, bool callee_complete, outputStream* st = tty);
 188 
 189 #define assert_pfl(p, ...) \
 190 do {                                           \
 191   if (!(p)) {                                  \
 192     JavaThread* t = JavaThread::active();      \
 193     if (t->has_last_Java_frame()) {            \
 194       tty->print_cr("assert(" #p ") failed:"); \
 195       t->print_frame_layout();                 \
 196     }                                          \
 197   }                                            \
 198   vmassert(p, __VA_ARGS__);                    \
 199 } while(0)
 200 
 201 #else
 202 static void verify_continuation(oop continuation) { }
 203 #define assert_pfl(p, ...)
 204 #endif
 205 
 206 static freeze_result is_pinned0(JavaThread* thread, oop cont_scope, bool safepoint);
 207 template<typename ConfigT, bool preempt> static inline freeze_result freeze_internal(JavaThread* current, intptr_t* const sp);
 208 
 209 static inline int prepare_thaw_internal(JavaThread* thread, bool return_barrier);
 210 template<typename ConfigT> static inline intptr_t* thaw_internal(JavaThread* thread, const Continuation::thaw_kind kind);
 211 
 212 
 213 // Entry point to freeze. Transitions are handled manually
 214 // Called from gen_continuation_yield() in sharedRuntime_<cpu>.cpp through Continuation::freeze_entry();
 215 template<typename ConfigT>
 216 static JRT_BLOCK_ENTRY(int, freeze(JavaThread* current, intptr_t* sp))
 217   assert(sp == current->frame_anchor()->last_Java_sp(), "");
 218 
 219   if (current->raw_cont_fastpath() > current->last_continuation()->entry_sp() || current->raw_cont_fastpath() < sp) {
 220     current->set_cont_fastpath(nullptr);
 221   }
 222 
 223   return checked_cast<int>(ConfigT::freeze(current, sp));
 224 JRT_END
 225 
 226 JRT_LEAF(int, Continuation::prepare_thaw(JavaThread* thread, bool return_barrier))
 227   return prepare_thaw_internal(thread, return_barrier);
 228 JRT_END
 229 
 230 template<typename ConfigT>
 231 static JRT_LEAF(intptr_t*, thaw(JavaThread* thread, int kind))
 232   // TODO: JRT_LEAF and NoHandleMark is problematic for JFR events.
 233   // vFrameStreamCommon allocates Handles in RegisterMap for continuations.
 234   // Also the preemption case with JVMTI events enabled might safepoint so
 235   // undo the NoSafepointVerifier here and rely on handling by ContinuationWrapper.
 236   // JRT_ENTRY instead?
 237   ResetNoHandleMark rnhm;
 238   DEBUG_ONLY(PauseNoSafepointVerifier pnsv(&__nsv);)
 239 
 240   // we might modify the code cache via BarrierSetNMethod::nmethod_entry_barrier
 241   MACOS_AARCH64_ONLY(ThreadWXEnable __wx(WXWrite, thread));
 242   return ConfigT::thaw(thread, (Continuation::thaw_kind)kind);
 243 JRT_END
 244 
 245 JVM_ENTRY(jint, CONT_isPinned0(JNIEnv* env, jobject cont_scope)) {
 246   JavaThread* thread = JavaThread::thread_from_jni_environment(env);
 247   return is_pinned0(thread, JNIHandles::resolve(cont_scope), false);
 248 }
 249 JVM_END
 250 
 251 ///////////
 252 
 253 enum class oop_kind { NARROW, WIDE };
 254 template <oop_kind oops, typename BarrierSetT>
 255 class Config {
 256 public:
 257   typedef Config<oops, BarrierSetT> SelfT;
 258   using OopT = std::conditional_t<oops == oop_kind::NARROW, narrowOop, oop>;
 259 
 260   static freeze_result freeze(JavaThread* thread, intptr_t* const sp) {
 261     freeze_result res = freeze_internal<SelfT, false>(thread, sp);
 262     JFR_ONLY(assert((res == freeze_ok) || (res == thread->last_freeze_fail_result()), "freeze failure not set"));
 263     return res;
 264   }
 265 
 266   static freeze_result freeze_preempt(JavaThread* thread, intptr_t* const sp) {
 267     return freeze_internal<SelfT, true>(thread, sp);
 268   }
 269 
 270   static intptr_t* thaw(JavaThread* thread, Continuation::thaw_kind kind) {
 271     return thaw_internal<SelfT>(thread, kind);
 272   }
 273 };
 274 
 275 #ifdef _WINDOWS
 276 static void map_stack_pages(JavaThread* thread, size_t size, address sp) {
 277   address new_sp = sp - size;
 278   address watermark = thread->stack_overflow_state()->shadow_zone_growth_watermark();
 279 
 280   if (new_sp < watermark) {
 281     size_t page_size = os::vm_page_size();
 282     address last_touched_page = watermark - StackOverflow::stack_shadow_zone_size();
 283     size_t pages_to_touch = align_up(watermark - new_sp, page_size) / page_size;
 284     while (pages_to_touch-- > 0) {
 285       last_touched_page -= page_size;
 286       *last_touched_page = 0;
 287     }
 288     thread->stack_overflow_state()->set_shadow_zone_growth_watermark(new_sp);
 289   }
 290 }
 291 #endif
 292 
 293 static bool stack_overflow_check(JavaThread* thread, size_t size, address sp) {
 294   const size_t page_size = os::vm_page_size();
 295   if (size > page_size) {
 296     if (sp - size < thread->stack_overflow_state()->shadow_zone_safe_limit()) {
 297       return false;
 298     }
 299     WINDOWS_ONLY(map_stack_pages(thread, size, sp));
 300   }
 301   return true;
 302 }
 303 
 304 #ifdef ASSERT
 305 static oop get_continuation(JavaThread* thread) {
 306   assert(thread != nullptr, "");
 307   assert(thread->threadObj() != nullptr, "");
 308   return java_lang_Thread::continuation(thread->threadObj());
 309 }
 310 #endif // ASSERT
 311 
 312 inline void clear_anchor(JavaThread* thread) {
 313   thread->frame_anchor()->clear();
 314 }
 315 
 316 static void set_anchor(JavaThread* thread, intptr_t* sp, address pc) {
 317   assert(pc != nullptr, "");
 318 
 319   JavaFrameAnchor* anchor = thread->frame_anchor();
 320   anchor->set_last_Java_sp(sp);
 321   anchor->set_last_Java_pc(pc);
 322   ContinuationHelper::set_anchor_pd(anchor, sp);
 323 
 324   assert(thread->has_last_Java_frame(), "");
 325   assert(thread->last_frame().cb() != nullptr, "");
 326 }
 327 
 328 static void set_anchor(JavaThread* thread, intptr_t* sp) {
 329   address pc = ContinuationHelper::return_address_at(
 330            sp - frame::sender_sp_ret_address_offset());
 331   set_anchor(thread, sp, pc);
 332 }
 333 
 334 static void set_anchor_to_entry(JavaThread* thread, ContinuationEntry* entry) {
 335   JavaFrameAnchor* anchor = thread->frame_anchor();
 336   anchor->set_last_Java_sp(entry->entry_sp());
 337   anchor->set_last_Java_pc(entry->entry_pc());
 338   ContinuationHelper::set_anchor_to_entry_pd(anchor, entry);
 339 
 340   assert(thread->has_last_Java_frame(), "");
 341   assert(thread->last_frame().cb() != nullptr, "");
 342 }
 343 
 344 #if CONT_JFR
 345 class FreezeThawJfrInfo : public StackObj {
 346   short _e_size;
 347   short _e_num_interpreted_frames;
 348  public:
 349 
 350   FreezeThawJfrInfo() : _e_size(0), _e_num_interpreted_frames(0) {}
 351   inline void record_interpreted_frame() { _e_num_interpreted_frames++; }
 352   inline void record_size_copied(int size) { _e_size += size << LogBytesPerWord; }
 353   template<typename Event> void post_jfr_event(Event *e, oop continuation, JavaThread* jt);
 354 };
 355 
 356 template<typename Event> void FreezeThawJfrInfo::post_jfr_event(Event* e, oop continuation, JavaThread* jt) {
 357   if (e->should_commit()) {
 358     log_develop_trace(continuations)("JFR event: iframes: %d size: %d", _e_num_interpreted_frames, _e_size);
 359     e->set_carrierThread(JFR_JVM_THREAD_ID(jt));
 360     e->set_continuationClass(continuation->klass());
 361     e->set_interpretedFrames(_e_num_interpreted_frames);
 362     e->set_size(_e_size);
 363     e->commit();
 364   }
 365 }
 366 #endif // CONT_JFR
 367 
 368 /////////////// FREEZE ////
 369 
 370 class FreezeBase : public StackObj {
 371 protected:
 372   JavaThread* const _thread;
 373   ContinuationWrapper& _cont;
 374   bool _barriers; // only set when we allocate a chunk
 375 
 376   intptr_t* _bottom_address;
 377 
 378   // Used for preemption only
 379   const bool _preempt;
 380   frame _last_frame;
 381 
 382   // Used to support freezing with held monitors
 383   int _monitors_in_lockstack;
 384 
 385   int _freeze_size; // total size of all frames plus metadata in words.
 386   int _total_align_size;
 387 
 388   intptr_t* _cont_stack_top;
 389   intptr_t* _cont_stack_bottom;
 390 
 391   CONT_JFR_ONLY(FreezeThawJfrInfo _jfr_info;)
 392 
 393 #ifdef ASSERT
 394   intptr_t* _orig_chunk_sp;
 395   int _fast_freeze_size;
 396   bool _empty;
 397 #endif
 398 
 399   JvmtiSampledObjectAllocEventCollector* _jvmti_event_collector;
 400 
 401   NOT_PRODUCT(int _frames;)
 402   DEBUG_ONLY(intptr_t* _last_write;)
 403 
 404   inline FreezeBase(JavaThread* thread, ContinuationWrapper& cont, intptr_t* sp, bool preempt);
 405 
 406 public:
 407   NOINLINE freeze_result freeze_slow();
 408   void freeze_fast_existing_chunk();
 409 
 410   CONT_JFR_ONLY(FreezeThawJfrInfo& jfr_info() { return _jfr_info; })
 411   void set_jvmti_event_collector(JvmtiSampledObjectAllocEventCollector* jsoaec) { _jvmti_event_collector = jsoaec; }
 412 
 413   inline int size_if_fast_freeze_available();
 414 
 415   inline frame& last_frame() { return _last_frame; }
 416 
 417 #ifdef ASSERT
 418   bool check_valid_fast_path();
 419 #endif
 420 
 421 protected:
 422   inline void init_rest();
 423   void throw_stack_overflow_on_humongous_chunk();
 424 
 425   // fast path
 426   inline void copy_to_chunk(intptr_t* from, intptr_t* to, int size);
 427   inline void unwind_frames();
 428   inline void patch_stack_pd(intptr_t* frame_sp, intptr_t* heap_sp);
 429 
 430   // slow path
 431   virtual stackChunkOop allocate_chunk_slow(size_t stack_size, int argsize_md) = 0;
 432 
 433   int cont_size() { return pointer_delta_as_int(_cont_stack_bottom, _cont_stack_top); }
 434 
 435 private:
 436   // slow path
 437   frame freeze_start_frame();
 438   frame freeze_start_frame_on_preempt();
 439   NOINLINE freeze_result recurse_freeze(frame& f, frame& caller, int callee_argsize, bool callee_interpreted, bool top);
 440   inline frame freeze_start_frame_yield_stub();
 441   template<typename FKind>
 442   inline freeze_result recurse_freeze_java_frame(const frame& f, frame& caller, int fsize, int argsize);
 443   inline void before_freeze_java_frame(const frame& f, const frame& caller, int fsize, int argsize, bool is_bottom_frame);
 444   inline void after_freeze_java_frame(const frame& hf, bool is_bottom_frame);
 445   freeze_result finalize_freeze(const frame& callee, frame& caller, int argsize);
 446   void patch(const frame& f, frame& hf, const frame& caller, bool is_bottom_frame);
 447   NOINLINE freeze_result recurse_freeze_interpreted_frame(frame& f, frame& caller, int callee_argsize, bool callee_interpreted);
 448   freeze_result recurse_freeze_compiled_frame(frame& f, frame& caller, int callee_argsize, bool callee_interpreted);
 449   NOINLINE freeze_result recurse_freeze_stub_frame(frame& f, frame& caller);
 450   NOINLINE freeze_result recurse_freeze_native_frame(frame& f, frame& caller);
 451   NOINLINE void finish_freeze(const frame& f, const frame& top);
 452 
 453   void freeze_lockstack(stackChunkOop chunk);
 454 
 455   inline bool stack_overflow();
 456 
 457   static frame sender(const frame& f) { return f.is_interpreted_frame() ? sender<ContinuationHelper::InterpretedFrame>(f)
 458                                                                         : sender<ContinuationHelper::NonInterpretedUnknownFrame>(f); }
 459   template<typename FKind> static inline frame sender(const frame& f);
 460   template<typename FKind> frame new_heap_frame(frame& f, frame& caller, int size_adjust = 0);
 461   inline void set_top_frame_metadata_pd(const frame& hf);
 462   inline void patch_pd(frame& callee, const frame& caller, bool is_bottom_frame);
 463   inline void patch_pd_unused(intptr_t* sp);
 464   void adjust_interpreted_frame_unextended_sp(frame& f);
 465   static inline void prepare_freeze_interpreted_top_frame(frame& f);
 466   static inline void relativize_interpreted_frame_metadata(const frame& f, const frame& hf);
 467 
 468 protected:
 469   void freeze_fast_copy(stackChunkOop chunk, int chunk_start_sp CONT_JFR_ONLY(COMMA bool chunk_is_allocated));
 470   bool freeze_fast_new_chunk(stackChunkOop chunk);
 471 };
 472 
 473 template <typename ConfigT>
 474 class Freeze : public FreezeBase {
 475 private:
 476   stackChunkOop allocate_chunk(size_t stack_size, int argsize_md);
 477 
 478 public:
 479   inline Freeze(JavaThread* thread, ContinuationWrapper& cont, intptr_t* frame_sp, bool preempt)
 480     : FreezeBase(thread, cont, frame_sp, preempt) {}
 481 
 482   freeze_result try_freeze_fast();
 483 
 484 protected:
 485   virtual stackChunkOop allocate_chunk_slow(size_t stack_size, int argsize_md) override { return allocate_chunk(stack_size, argsize_md); }
 486 };
 487 
 488 FreezeBase::FreezeBase(JavaThread* thread, ContinuationWrapper& cont, intptr_t* frame_sp, bool preempt) :
 489     _thread(thread), _cont(cont), _barriers(false), _preempt(preempt), _last_frame(false /* no initialization */) {
 490   DEBUG_ONLY(_jvmti_event_collector = nullptr;)
 491 
 492   assert(_thread != nullptr, "");
 493   assert(_thread->last_continuation()->entry_sp() == _cont.entrySP(), "");
 494 
 495   DEBUG_ONLY(_cont.entry()->verify_cookie();)
 496 
 497   assert(!Interpreter::contains(_cont.entryPC()), "");
 498 
 499   _bottom_address = _cont.entrySP() - _cont.entry_frame_extension();
 500 #ifdef _LP64
 501   if (((intptr_t)_bottom_address & 0xf) != 0) {
 502     _bottom_address--;
 503   }
 504   assert(is_aligned(_bottom_address, frame::frame_alignment), "");
 505 #endif
 506 
 507   log_develop_trace(continuations)("bottom_address: " INTPTR_FORMAT " entrySP: " INTPTR_FORMAT " argsize: " PTR_FORMAT,
 508                 p2i(_bottom_address), p2i(_cont.entrySP()), (_cont.entrySP() - _bottom_address) << LogBytesPerWord);
 509   assert(_bottom_address != nullptr, "");
 510   assert(_bottom_address <= _cont.entrySP(), "");
 511   DEBUG_ONLY(_last_write = nullptr;)
 512 
 513   assert(_cont.chunk_invariant(), "");
 514   assert(!Interpreter::contains(_cont.entryPC()), "");
 515 #if !defined(PPC64) || defined(ZERO)
 516   static const int doYield_stub_frame_size = frame::metadata_words;
 517 #else
 518   static const int doYield_stub_frame_size = frame::native_abi_reg_args_size >> LogBytesPerWord;
 519 #endif
 520   // With preemption doYield() might not have been resolved yet
 521   assert(_preempt || SharedRuntime::cont_doYield_stub()->frame_size() == doYield_stub_frame_size, "");
 522 
 523   if (preempt) {
 524     _last_frame = _thread->last_frame();
 525   }
 526 
 527   // properties of the continuation on the stack; all sizes are in words
 528   _cont_stack_top    = frame_sp + (!preempt ? doYield_stub_frame_size : 0); // we don't freeze the doYield stub frame
 529   _cont_stack_bottom = _cont.entrySP() + (_cont.argsize() == 0 ? frame::metadata_words_at_top : 0)
 530       - ContinuationHelper::frame_align_words(_cont.argsize()); // see alignment in thaw
 531 
 532   log_develop_trace(continuations)("freeze size: %d argsize: %d top: " INTPTR_FORMAT " bottom: " INTPTR_FORMAT,
 533     cont_size(), _cont.argsize(), p2i(_cont_stack_top), p2i(_cont_stack_bottom));
 534   assert(cont_size() > 0, "");
 535 
 536   _monitors_in_lockstack = _thread->lock_stack().monitor_count();
 537 }
 538 
 539 void FreezeBase::init_rest() { // we want to postpone some initialization after chunk handling
 540   _freeze_size = 0;
 541   _total_align_size = 0;
 542   NOT_PRODUCT(_frames = 0;)
 543 }
 544 
 545 void FreezeBase::freeze_lockstack(stackChunkOop chunk) {
 546   assert(chunk->sp_address() - chunk->start_address() >= _monitors_in_lockstack, "no room for lockstack");
 547 
 548   _thread->lock_stack().move_to_address((oop*)chunk->start_address());
 549   chunk->set_lockstack_size(checked_cast<uint8_t>(_monitors_in_lockstack));
 550   chunk->set_has_lockstack(true);
 551 }
 552 
 553 void FreezeBase::copy_to_chunk(intptr_t* from, intptr_t* to, int size) {
 554   stackChunkOop chunk = _cont.tail();
 555   chunk->copy_from_stack_to_chunk(from, to, size);
 556   CONT_JFR_ONLY(_jfr_info.record_size_copied(size);)
 557 
 558 #ifdef ASSERT
 559   if (_last_write != nullptr) {
 560     assert(_last_write == to + size, "Missed a spot: _last_write: " INTPTR_FORMAT " to+size: " INTPTR_FORMAT
 561         " stack_size: %d _last_write offset: " PTR_FORMAT " to+size: " PTR_FORMAT, p2i(_last_write), p2i(to+size),
 562         chunk->stack_size(), _last_write-chunk->start_address(), to+size-chunk->start_address());
 563     _last_write = to;
 564   }
 565 #endif
 566 }
 567 
 568 static void assert_frames_in_continuation_are_safe(JavaThread* thread) {
 569 #ifdef ASSERT
 570   StackWatermark* watermark = StackWatermarkSet::get(thread, StackWatermarkKind::gc);
 571   if (watermark == nullptr) {
 572     return;
 573   }
 574   ContinuationEntry* ce = thread->last_continuation();
 575   RegisterMap map(thread,
 576                   RegisterMap::UpdateMap::include,
 577                   RegisterMap::ProcessFrames::skip,
 578                   RegisterMap::WalkContinuation::skip);
 579   map.set_include_argument_oops(false);
 580   for (frame f = thread->last_frame(); Continuation::is_frame_in_continuation(ce, f); f = f.sender(&map)) {
 581     watermark->assert_is_frame_safe(f);
 582   }
 583 #endif // ASSERT
 584 }
 585 
 586 // Called _after_ the last possible safepoint during the freeze operation (chunk allocation)
 587 void FreezeBase::unwind_frames() {
 588   ContinuationEntry* entry = _cont.entry();
 589   entry->flush_stack_processing(_thread);
 590   assert_frames_in_continuation_are_safe(_thread);
 591   JFR_ONLY(Jfr::check_and_process_sample_request(_thread);)
 592   set_anchor_to_entry(_thread, entry);
 593 }
 594 
 595 template <typename ConfigT>
 596 freeze_result Freeze<ConfigT>::try_freeze_fast() {
 597   assert(_thread->thread_state() == _thread_in_vm, "");
 598   assert(_thread->cont_fastpath(), "");
 599 
 600   DEBUG_ONLY(_fast_freeze_size = size_if_fast_freeze_available();)
 601   assert(_fast_freeze_size == 0, "");
 602 
 603   stackChunkOop chunk = allocate_chunk(cont_size() + frame::metadata_words + _monitors_in_lockstack, _cont.argsize() + frame::metadata_words_at_top);
 604   if (freeze_fast_new_chunk(chunk)) {
 605     return freeze_ok;
 606   }
 607   if (_thread->has_pending_exception()) {
 608     return freeze_exception;
 609   }
 610 
 611   // TODO R REMOVE when deopt change is fixed
 612   assert(!_thread->cont_fastpath() || _barriers, "");
 613   log_develop_trace(continuations)("-- RETRYING SLOW --");
 614   return freeze_slow();
 615 }
 616 
 617 // Returns size needed if the continuation fits, otherwise 0.
 618 int FreezeBase::size_if_fast_freeze_available() {
 619   stackChunkOop chunk = _cont.tail();
 620   if (chunk == nullptr || chunk->is_gc_mode() || chunk->requires_barriers() || chunk->has_mixed_frames()) {
 621     log_develop_trace(continuations)("chunk available %s", chunk == nullptr ? "no chunk" : "chunk requires barriers");
 622     return 0;
 623   }
 624 
 625   int total_size_needed = cont_size();
 626   const int chunk_sp = chunk->sp();
 627 
 628   // argsize can be nonzero if we have a caller, but the caller could be in a non-empty parent chunk,
 629   // so we subtract it only if we overlap with the caller, i.e. the current chunk isn't empty.
 630   // Consider leaving the chunk's argsize set when emptying it and removing the following branch,
 631   // although that would require changing stackChunkOopDesc::is_empty
 632   if (!chunk->is_empty()) {
 633     total_size_needed -= _cont.argsize() + frame::metadata_words_at_top;
 634   }
 635 
 636   total_size_needed += _monitors_in_lockstack;
 637 
 638   int chunk_free_room = chunk_sp - frame::metadata_words_at_bottom;
 639   bool available = chunk_free_room >= total_size_needed;
 640   log_develop_trace(continuations)("chunk available: %s size: %d argsize: %d top: " INTPTR_FORMAT " bottom: " INTPTR_FORMAT,
 641     available ? "yes" : "no" , total_size_needed, _cont.argsize(), p2i(_cont_stack_top), p2i(_cont_stack_bottom));
 642   return available ? total_size_needed : 0;
 643 }
 644 
 645 void FreezeBase::freeze_fast_existing_chunk() {
 646   stackChunkOop chunk = _cont.tail();
 647 
 648   DEBUG_ONLY(_fast_freeze_size = size_if_fast_freeze_available();)
 649   assert(_fast_freeze_size > 0, "");
 650 
 651   if (!chunk->is_empty()) { // we are copying into a non-empty chunk
 652     DEBUG_ONLY(_empty = false;)
 653     DEBUG_ONLY(_orig_chunk_sp = chunk->sp_address();)
 654 #ifdef ASSERT
 655     {
 656       intptr_t* retaddr_slot = (chunk->sp_address()
 657                                 - frame::sender_sp_ret_address_offset());
 658       assert(ContinuationHelper::return_address_at(retaddr_slot) == chunk->pc(),
 659              "unexpected saved return address");
 660     }
 661 #endif
 662 
 663     // the chunk's sp before the freeze, adjusted to point beyond the stack-passed arguments in the topmost frame
 664     // we overlap; we'll overwrite the chunk's top frame's callee arguments
 665     const int chunk_start_sp = chunk->sp() + _cont.argsize() + frame::metadata_words_at_top;
 666     assert(chunk_start_sp <= chunk->stack_size(), "sp not pointing into stack");
 667 
 668     // increase max_size by what we're freezing minus the overlap
 669     chunk->set_max_thawing_size(chunk->max_thawing_size() + cont_size() - _cont.argsize() - frame::metadata_words_at_top);
 670 
 671     intptr_t* const bottom_sp = _cont_stack_bottom - _cont.argsize() - frame::metadata_words_at_top;
 672     assert(bottom_sp == _bottom_address, "");
 673     // Because the chunk isn't empty, we know there's a caller in the chunk, therefore the bottom-most frame
 674     // should have a return barrier (installed back when we thawed it).
 675 #ifdef ASSERT
 676     {
 677       intptr_t* retaddr_slot = (bottom_sp
 678                                 - frame::sender_sp_ret_address_offset());
 679       assert(ContinuationHelper::return_address_at(retaddr_slot)
 680              == StubRoutines::cont_returnBarrier(),
 681              "should be the continuation return barrier");
 682     }
 683 #endif
 684     // We copy the fp from the chunk back to the stack because it contains some caller data,
 685     // including, possibly, an oop that might have gone stale since we thawed.
 686     patch_stack_pd(bottom_sp, chunk->sp_address());
 687     // we don't patch the return pc at this time, so as not to make the stack unwalkable for async walks
 688 
 689     freeze_fast_copy(chunk, chunk_start_sp CONT_JFR_ONLY(COMMA false));
 690   } else { // the chunk is empty
 691     const int chunk_start_sp = chunk->stack_size();
 692 
 693     DEBUG_ONLY(_empty = true;)
 694     DEBUG_ONLY(_orig_chunk_sp = chunk->start_address() + chunk_start_sp;)
 695 
 696     chunk->set_max_thawing_size(cont_size());
 697     chunk->set_bottom(chunk_start_sp - _cont.argsize() - frame::metadata_words_at_top);
 698     chunk->set_sp(chunk->bottom());
 699 
 700     freeze_fast_copy(chunk, chunk_start_sp CONT_JFR_ONLY(COMMA false));
 701   }
 702 }
 703 
 704 bool FreezeBase::freeze_fast_new_chunk(stackChunkOop chunk) {
 705   DEBUG_ONLY(_empty = true;)
 706 
 707   // Install new chunk
 708   _cont.set_tail(chunk);
 709 
 710   if (UNLIKELY(chunk == nullptr || !_thread->cont_fastpath() || _barriers)) { // OOME/probably humongous
 711     log_develop_trace(continuations)("Retrying slow. Barriers: %d", _barriers);
 712     return false;
 713   }
 714 
 715   chunk->set_max_thawing_size(cont_size());
 716 
 717   // in a fresh chunk, we freeze *with* the bottom-most frame's stack arguments.
 718   // They'll then be stored twice: in the chunk and in the parent chunk's top frame
 719   const int chunk_start_sp = cont_size() + frame::metadata_words + _monitors_in_lockstack;
 720   assert(chunk_start_sp == chunk->stack_size(), "");
 721 
 722   DEBUG_ONLY(_orig_chunk_sp = chunk->start_address() + chunk_start_sp;)
 723 
 724   freeze_fast_copy(chunk, chunk_start_sp CONT_JFR_ONLY(COMMA true));
 725 
 726   return true;
 727 }
 728 
 729 void FreezeBase::freeze_fast_copy(stackChunkOop chunk, int chunk_start_sp CONT_JFR_ONLY(COMMA bool chunk_is_allocated)) {
 730   assert(chunk != nullptr, "");
 731   assert(!chunk->has_mixed_frames(), "");
 732   assert(!chunk->is_gc_mode(), "");
 733   assert(!chunk->has_bitmap(), "");
 734   assert(!chunk->requires_barriers(), "");
 735   assert(chunk == _cont.tail(), "");
 736 
 737   // We unwind frames after the last safepoint so that the GC will have found the oops in the frames, but before
 738   // writing into the chunk. This is so that an asynchronous stack walk (not at a safepoint) that suspends us here
 739   // will either see no continuation on the stack, or a consistent chunk.
 740   unwind_frames();
 741 
 742   log_develop_trace(continuations)("freeze_fast start: chunk " INTPTR_FORMAT " size: %d orig sp: %d argsize: %d",
 743     p2i((oopDesc*)chunk), chunk->stack_size(), chunk_start_sp, _cont.argsize());
 744   assert(chunk_start_sp <= chunk->stack_size(), "");
 745   assert(chunk_start_sp >= cont_size(), "no room in the chunk");
 746 
 747   const int chunk_new_sp = chunk_start_sp - cont_size(); // the chunk's new sp, after freeze
 748   assert(!(_fast_freeze_size > 0) || (_orig_chunk_sp - (chunk->start_address() + chunk_new_sp)) == (_fast_freeze_size - _monitors_in_lockstack), "");
 749 
 750   intptr_t* chunk_top = chunk->start_address() + chunk_new_sp;
 751 #ifdef ASSERT
 752   if (!_empty) {
 753     intptr_t* retaddr_slot = (_orig_chunk_sp
 754                               - frame::sender_sp_ret_address_offset());
 755     assert(ContinuationHelper::return_address_at(retaddr_slot) == chunk->pc(),
 756            "unexpected saved return address");
 757   }
 758 #endif
 759 
 760   log_develop_trace(continuations)("freeze_fast start: " INTPTR_FORMAT " sp: %d chunk_top: " INTPTR_FORMAT,
 761                               p2i(chunk->start_address()), chunk_new_sp, p2i(chunk_top));
 762 
 763   int adjust = frame::metadata_words_at_bottom;
 764 #if INCLUDE_ASAN && defined(AARCH64)
 765   // Reading at offset frame::metadata_words_at_bottom from _cont_stack_top
 766   // will accesss memory at the callee frame, which on preemption cases will
 767   // be the VM native method being called. The Arm 64-bit ABI doesn't specify
 768   // a location where the frame record (returnpc+fp) has to be stored within
 769   // a stack frame, and GCC currently chooses to save it at the top of the
 770   // frame (lowest address). ASan treats this memory access in the callee as
 771   // an overflow access to one of the locals stored in that frame. For these
 772   // preemption cases we don't need to read these words anyways so we avoid it.
 773   if (_preempt) {
 774     adjust = 0;
 775   }
 776 #endif
 777   intptr_t* from = _cont_stack_top - adjust;
 778   intptr_t* to   = chunk_top - adjust;
 779   copy_to_chunk(from, to, cont_size() + adjust);
 780   // Because we're not patched yet, the chunk is now in a bad state
 781 
 782   // patch return pc of the bottom-most frozen frame (now in the chunk)
 783   // with the actual caller's return address
 784   intptr_t* chunk_bottom_retaddr_slot = (chunk_top + cont_size()
 785                                          - _cont.argsize()
 786                                          - frame::metadata_words_at_top
 787                                          - frame::sender_sp_ret_address_offset());
 788 #ifdef ASSERT
 789   if (!_empty) {
 790     assert(ContinuationHelper::return_address_at(chunk_bottom_retaddr_slot)
 791            == StubRoutines::cont_returnBarrier(),
 792            "should be the continuation return barrier");
 793   }
 794 #endif
 795   ContinuationHelper::patch_return_address_at(chunk_bottom_retaddr_slot,
 796                                               chunk->pc());
 797 
 798   // We're always writing to a young chunk, so the GC can't see it until the next safepoint.
 799   chunk->set_sp(chunk_new_sp);
 800 
 801   // set chunk->pc to the return address of the topmost frame in the chunk
 802   if (_preempt) {
 803     // On aarch64/riscv64, the return pc of the top frame won't necessarily be at sp[-1].
 804     // Also, on x64, if the top frame is the native wrapper frame, sp[-1] will not
 805     // be the pc we used when creating the oopmap. Get the top's frame last pc from
 806     // the anchor instead.
 807     address last_pc = _last_frame.pc();
 808     ContinuationHelper::patch_return_address_at(chunk_top - frame::sender_sp_ret_address_offset(), last_pc);
 809     chunk->set_pc(last_pc);
 810     // For stub/native frames the fp is not used while frozen, and will be constructed
 811     // again when thawing the frame (see ThawBase::handle_preempted_continuation). We
 812     // patch it with a special bad address to help with debugging, particularly when
 813     // inspecting frames and identifying invalid accesses.
 814     patch_pd_unused(chunk_top);
 815   } else {
 816     chunk->set_pc(ContinuationHelper::return_address_at(
 817                   _cont_stack_top - frame::sender_sp_ret_address_offset()));
 818   }
 819 
 820   if (_monitors_in_lockstack > 0) {
 821     freeze_lockstack(chunk);
 822   }
 823 
 824   _cont.write();
 825 
 826   log_develop_trace(continuations)("FREEZE CHUNK #" INTPTR_FORMAT " (young)", _cont.hash());
 827   LogTarget(Trace, continuations) lt;
 828   if (lt.develop_is_enabled()) {
 829     LogStream ls(lt);
 830     chunk->print_on(true, &ls);
 831   }
 832 
 833   // Verification
 834   assert(_cont.chunk_invariant(), "");
 835   chunk->verify();
 836 
 837 #if CONT_JFR
 838   EventContinuationFreezeFast e;
 839   if (e.should_commit()) {
 840     e.set_id(cast_from_oop<u8>(chunk));
 841     DEBUG_ONLY(e.set_allocate(chunk_is_allocated);)
 842     e.set_size(cont_size() << LogBytesPerWord);
 843     e.commit();
 844   }
 845 #endif
 846 }
 847 
 848 NOINLINE freeze_result FreezeBase::freeze_slow() {
 849 #ifdef ASSERT
 850   ResourceMark rm;
 851 #endif
 852 
 853   log_develop_trace(continuations)("freeze_slow  #" INTPTR_FORMAT, _cont.hash());
 854   assert(_thread->thread_state() == _thread_in_vm || _thread->thread_state() == _thread_blocked, "");
 855 
 856 #if CONT_JFR
 857   EventContinuationFreezeSlow e;
 858   if (e.should_commit()) {
 859     e.set_id(cast_from_oop<u8>(_cont.continuation()));
 860     e.commit();
 861   }
 862 #endif
 863 
 864   init_rest();
 865 
 866   HandleMark hm(Thread::current());
 867 
 868   frame f = freeze_start_frame();
 869 
 870   LogTarget(Debug, continuations) lt;
 871   if (lt.develop_is_enabled()) {
 872     LogStream ls(lt);
 873     f.print_on(&ls);
 874   }
 875 
 876   frame caller; // the frozen caller in the chunk
 877   freeze_result res = recurse_freeze(f, caller, 0, false, true);
 878 
 879   if (res == freeze_ok) {
 880     finish_freeze(f, caller);
 881     _cont.write();
 882   }
 883 
 884   return res;
 885 }
 886 
 887 frame FreezeBase::freeze_start_frame() {
 888   if (LIKELY(!_preempt)) {
 889     return freeze_start_frame_yield_stub();
 890   } else {
 891     return freeze_start_frame_on_preempt();
 892   }
 893 }
 894 
 895 frame FreezeBase::freeze_start_frame_yield_stub() {
 896   frame f = _thread->last_frame();
 897   assert(SharedRuntime::cont_doYield_stub()->contains(f.pc()), "must be");
 898   f = sender<ContinuationHelper::NonInterpretedUnknownFrame>(f);
 899   assert(Continuation::is_frame_in_continuation(_thread->last_continuation(), f), "");
 900   return f;
 901 }
 902 
 903 frame FreezeBase::freeze_start_frame_on_preempt() {
 904   assert(_last_frame.sp() == _thread->last_frame().sp(), "_last_frame should be already initialized");
 905   assert(Continuation::is_frame_in_continuation(_thread->last_continuation(), _last_frame), "");
 906   return _last_frame;
 907 }
 908 
 909 // The parameter callee_argsize includes metadata that has to be part of caller/callee overlap.
 910 NOINLINE freeze_result FreezeBase::recurse_freeze(frame& f, frame& caller, int callee_argsize, bool callee_interpreted, bool top) {
 911   assert(f.unextended_sp() < _bottom_address, ""); // see recurse_freeze_java_frame
 912   assert(f.is_interpreted_frame() || ((top && _preempt) == ContinuationHelper::Frame::is_stub(f.cb()))
 913          || ((top && _preempt) == f.is_native_frame()), "");
 914 
 915   if (stack_overflow()) {
 916     return freeze_exception;
 917   }
 918 
 919   if (f.is_compiled_frame()) {
 920     if (UNLIKELY(f.oop_map() == nullptr)) {
 921       // special native frame
 922       return freeze_pinned_native;
 923     }
 924     return recurse_freeze_compiled_frame(f, caller, callee_argsize, callee_interpreted);
 925   } else if (f.is_interpreted_frame()) {
 926     assert(!f.interpreter_frame_method()->is_native() || (top && _preempt), "");
 927     return recurse_freeze_interpreted_frame(f, caller, callee_argsize, callee_interpreted);
 928   } else if (top && _preempt) {
 929     assert(f.is_native_frame() || f.is_runtime_frame(), "");
 930     return f.is_native_frame() ? recurse_freeze_native_frame(f, caller) : recurse_freeze_stub_frame(f, caller);
 931   } else {
 932     // Frame can't be frozen. Most likely the call_stub or upcall_stub
 933     // which indicates there are further natives frames up the stack.
 934     return freeze_pinned_native;
 935   }
 936 }
 937 
 938 // The parameter callee_argsize includes metadata that has to be part of caller/callee overlap.
 939 // See also StackChunkFrameStream<frame_kind>::frame_size()
 940 template<typename FKind>
 941 inline freeze_result FreezeBase::recurse_freeze_java_frame(const frame& f, frame& caller, int fsize, int argsize) {
 942   assert(FKind::is_instance(f), "");
 943 
 944   assert(fsize > 0, "");
 945   assert(argsize >= 0, "");
 946   _freeze_size += fsize;
 947   NOT_PRODUCT(_frames++;)
 948 
 949   assert(FKind::frame_bottom(f) <= _bottom_address, "");
 950 
 951   // We don't use FKind::frame_bottom(f) == _bottom_address because on x64 there's sometimes an extra word between
 952   // enterSpecial and an interpreted frame
 953   if (FKind::frame_bottom(f) >= _bottom_address - 1) {
 954     return finalize_freeze(f, caller, argsize); // recursion end
 955   } else {
 956     frame senderf = sender<FKind>(f);
 957     assert(FKind::interpreted || senderf.sp() == senderf.unextended_sp(), "");
 958     freeze_result result = recurse_freeze(senderf, caller, argsize, FKind::interpreted, false); // recursive call
 959     return result;
 960   }
 961 }
 962 
 963 inline void FreezeBase::before_freeze_java_frame(const frame& f, const frame& caller, int fsize, int argsize, bool is_bottom_frame) {
 964   LogTarget(Trace, continuations) lt;
 965   if (lt.develop_is_enabled()) {
 966     LogStream ls(lt);
 967     ls.print_cr("======== FREEZING FRAME interpreted: %d bottom: %d", f.is_interpreted_frame(), is_bottom_frame);
 968     ls.print_cr("fsize: %d argsize: %d", fsize, argsize);
 969     f.print_value_on(&ls);
 970   }
 971   assert(caller.is_interpreted_frame() == Interpreter::contains(caller.pc()), "");
 972 }
 973 
 974 inline void FreezeBase::after_freeze_java_frame(const frame& hf, bool is_bottom_frame) {
 975   LogTarget(Trace, continuations) lt;
 976   if (lt.develop_is_enabled()) {
 977     LogStream ls(lt);
 978     DEBUG_ONLY(hf.print_value_on(&ls);)
 979     assert(hf.is_heap_frame(), "should be");
 980     DEBUG_ONLY(print_frame_layout(hf, false, &ls);)
 981     if (is_bottom_frame) {
 982       ls.print_cr("bottom h-frame:");
 983       hf.print_on(&ls);
 984     }
 985   }
 986 }
 987 
 988 // The parameter argsize_md includes metadata that has to be part of caller/callee overlap.
 989 // See also StackChunkFrameStream<frame_kind>::frame_size()
 990 freeze_result FreezeBase::finalize_freeze(const frame& callee, frame& caller, int argsize_md) {
 991   int argsize = argsize_md - frame::metadata_words_at_top;
 992   assert(callee.is_interpreted_frame()
 993     || ContinuationHelper::Frame::is_stub(callee.cb())
 994     || callee.cb()->as_nmethod()->is_osr_method()
 995     || argsize == _cont.argsize(), "argsize: %d cont.argsize: %d", argsize, _cont.argsize());
 996   log_develop_trace(continuations)("bottom: " INTPTR_FORMAT " count %d size: %d argsize: %d",
 997     p2i(_bottom_address), _frames, _freeze_size << LogBytesPerWord, argsize);
 998 
 999   LogTarget(Trace, continuations) lt;
1000 
1001 #ifdef ASSERT
1002   bool empty = _cont.is_empty();
1003   log_develop_trace(continuations)("empty: %d", empty);
1004 #endif
1005 
1006   stackChunkOop chunk = _cont.tail();
1007 
1008   assert(chunk == nullptr || (chunk->max_thawing_size() == 0) == chunk->is_empty(), "");
1009 
1010   _freeze_size += frame::metadata_words; // for top frame's metadata
1011 
1012   int overlap = 0; // the args overlap the caller -- if there is one in this chunk and is of the same kind
1013   int unextended_sp = -1;
1014   if (chunk != nullptr) {
1015     if (!chunk->is_empty()) {
1016       StackChunkFrameStream<ChunkFrames::Mixed> last(chunk);
1017       unextended_sp = chunk->to_offset(StackChunkFrameStream<ChunkFrames::Mixed>(chunk).unextended_sp());
1018       bool top_interpreted = Interpreter::contains(chunk->pc());
1019       if (callee.is_interpreted_frame() == top_interpreted) {
1020         overlap = argsize_md;
1021       }
1022     } else {
1023       unextended_sp = chunk->stack_size() - frame::metadata_words_at_top;
1024     }
1025   }
1026 
1027   log_develop_trace(continuations)("finalize _size: %d overlap: %d unextended_sp: %d", _freeze_size, overlap, unextended_sp);
1028 
1029   _freeze_size -= overlap;
1030   assert(_freeze_size >= 0, "");
1031 
1032   assert(chunk == nullptr || chunk->is_empty()
1033           || unextended_sp == chunk->to_offset(StackChunkFrameStream<ChunkFrames::Mixed>(chunk).unextended_sp()), "");
1034   assert(chunk != nullptr || unextended_sp < _freeze_size, "");
1035 
1036   _freeze_size += _monitors_in_lockstack;
1037 
1038   // _barriers can be set to true by an allocation in freeze_fast, in which case the chunk is available
1039   bool allocated_old_in_freeze_fast = _barriers;
1040   assert(!allocated_old_in_freeze_fast || (unextended_sp >= _freeze_size && chunk->is_empty()),
1041     "Chunk allocated in freeze_fast is of insufficient size "
1042     "unextended_sp: %d size: %d is_empty: %d", unextended_sp, _freeze_size, chunk->is_empty());
1043   assert(!allocated_old_in_freeze_fast || (!UseZGC && !UseG1GC), "Unexpected allocation");
1044 
1045   DEBUG_ONLY(bool empty_chunk = true);
1046   if (unextended_sp < _freeze_size || chunk->is_gc_mode() || (!allocated_old_in_freeze_fast && chunk->requires_barriers())) {
1047     // ALLOCATE NEW CHUNK
1048 
1049     if (lt.develop_is_enabled()) {
1050       LogStream ls(lt);
1051       if (chunk == nullptr) {
1052         ls.print_cr("no chunk");
1053       } else {
1054         ls.print_cr("chunk barriers: %d _size: %d free size: %d",
1055           chunk->requires_barriers(), _freeze_size, chunk->sp() - frame::metadata_words);
1056         chunk->print_on(&ls);
1057       }
1058     }
1059 
1060     _freeze_size += overlap; // we're allocating a new chunk, so no overlap
1061     // overlap = 0;
1062 
1063     chunk = allocate_chunk_slow(_freeze_size, argsize_md);
1064     if (chunk == nullptr) {
1065       return freeze_exception;
1066     }
1067 
1068     // Install new chunk
1069     _cont.set_tail(chunk);
1070     assert(chunk->is_empty(), "");
1071   } else {
1072     // REUSE EXISTING CHUNK
1073     log_develop_trace(continuations)("Reusing chunk mixed: %d empty: %d", chunk->has_mixed_frames(), chunk->is_empty());
1074     if (chunk->is_empty()) {
1075       int sp = chunk->stack_size() - argsize_md;
1076       chunk->set_sp(sp);
1077       chunk->set_bottom(sp);
1078       _freeze_size += overlap;
1079       assert(chunk->max_thawing_size() == 0, "");
1080     } DEBUG_ONLY(else empty_chunk = false;)
1081   }
1082   assert(!chunk->is_gc_mode(), "");
1083   assert(!chunk->has_bitmap(), "");
1084   chunk->set_has_mixed_frames(true);
1085 
1086   assert(chunk->requires_barriers() == _barriers, "");
1087   assert(!_barriers || chunk->is_empty(), "");
1088 
1089   assert(!chunk->is_empty() || StackChunkFrameStream<ChunkFrames::Mixed>(chunk).is_done(), "");
1090   assert(!chunk->is_empty() || StackChunkFrameStream<ChunkFrames::Mixed>(chunk).to_frame().is_empty(), "");
1091 
1092   if (_preempt) {
1093     frame f = _thread->last_frame();
1094     if (f.is_interpreted_frame()) {
1095       // Some platforms do not save the last_sp in the top interpreter frame on VM calls.
1096       // We need it so that on resume we can restore the sp to the right place, since
1097       // thawing might add an alignment word to the expression stack (see finish_thaw()).
1098       // We do it now that we know freezing will be successful.
1099       prepare_freeze_interpreted_top_frame(f);
1100     }
1101   }
1102 
1103   // We unwind frames after the last safepoint so that the GC will have found the oops in the frames, but before
1104   // writing into the chunk. This is so that an asynchronous stack walk (not at a safepoint) that suspends us here
1105   // will either see no continuation or a consistent chunk.
1106   unwind_frames();
1107 
1108   chunk->set_max_thawing_size(chunk->max_thawing_size() + _freeze_size - _monitors_in_lockstack - frame::metadata_words);
1109 
1110   if (lt.develop_is_enabled()) {
1111     LogStream ls(lt);
1112     ls.print_cr("top chunk:");
1113     chunk->print_on(&ls);
1114   }
1115 
1116   if (_monitors_in_lockstack > 0) {
1117     freeze_lockstack(chunk);
1118   }
1119 
1120   // The topmost existing frame in the chunk; or an empty frame if the chunk is empty
1121   caller = StackChunkFrameStream<ChunkFrames::Mixed>(chunk).to_frame();
1122 
1123   DEBUG_ONLY(_last_write = caller.unextended_sp() + (empty_chunk ? argsize_md : overlap);)
1124 
1125   assert(chunk->is_in_chunk(_last_write - _freeze_size),
1126     "last_write-size: " INTPTR_FORMAT " start: " INTPTR_FORMAT, p2i(_last_write-_freeze_size), p2i(chunk->start_address()));
1127 #ifdef ASSERT
1128   if (lt.develop_is_enabled()) {
1129     LogStream ls(lt);
1130     ls.print_cr("top hframe before (freeze):");
1131     assert(caller.is_heap_frame(), "should be");
1132     caller.print_on(&ls);
1133   }
1134 
1135   assert(!empty || Continuation::is_continuation_entry_frame(callee, nullptr), "");
1136 
1137   frame entry = sender(callee);
1138 
1139   assert((!empty && Continuation::is_return_barrier_entry(entry.pc())) || (empty && Continuation::is_continuation_enterSpecial(entry)), "");
1140   assert(callee.is_interpreted_frame() || entry.sp() == entry.unextended_sp(), "");
1141 #endif
1142 
1143   return freeze_ok_bottom;
1144 }
1145 
1146 // After freezing a frame we need to possibly adjust some values related to the caller frame.
1147 void FreezeBase::patch(const frame& f, frame& hf, const frame& caller, bool is_bottom_frame) {
1148   if (is_bottom_frame) {
1149     // If we're the bottom frame, we need to replace the return barrier with the real
1150     // caller's pc.
1151     address last_pc = caller.pc();
1152     assert((last_pc == nullptr) == _cont.tail()->is_empty(), "");
1153     ContinuationHelper::Frame::patch_pc(caller, last_pc);
1154   } else {
1155     assert(!caller.is_empty(), "");
1156   }
1157 
1158   patch_pd(hf, caller, is_bottom_frame);
1159 
1160   if (f.is_interpreted_frame()) {
1161     assert(hf.is_heap_frame(), "should be");
1162     ContinuationHelper::InterpretedFrame::patch_sender_sp(hf, caller);
1163   }
1164 
1165 #ifdef ASSERT
1166   if (hf.is_compiled_frame()) {
1167     if (f.is_deoptimized_frame()) { // TODO DEOPT: long term solution: unroll on freeze and patch pc
1168       log_develop_trace(continuations)("Freezing deoptimized frame");
1169       assert(f.cb()->as_nmethod()->is_deopt_pc(f.raw_pc()), "");
1170       assert(f.cb()->as_nmethod()->is_deopt_pc(ContinuationHelper::Frame::real_pc(f)), "");
1171     }
1172   }
1173 #endif
1174 }
1175 
1176 #ifdef ASSERT
1177 static void verify_frame_top(const frame& f, intptr_t* top) {
1178   ResourceMark rm;
1179   InterpreterOopMap mask;
1180   f.interpreted_frame_oop_map(&mask);
1181   assert(top <= ContinuationHelper::InterpretedFrame::frame_top(f, &mask),
1182          "frame_top: " INTPTR_FORMAT " Interpreted::frame_top: " INTPTR_FORMAT,
1183            p2i(top), p2i(ContinuationHelper::InterpretedFrame::frame_top(f, &mask)));
1184 }
1185 #endif // ASSERT
1186 
1187 // The parameter callee_argsize includes metadata that has to be part of caller/callee overlap.
1188 // See also StackChunkFrameStream<frame_kind>::frame_size()
1189 NOINLINE freeze_result FreezeBase::recurse_freeze_interpreted_frame(frame& f, frame& caller,
1190                                                                     int callee_argsize /* incl. metadata */,
1191                                                                     bool callee_interpreted) {
1192   adjust_interpreted_frame_unextended_sp(f);
1193 
1194   // The frame's top never includes the stack arguments to the callee
1195   intptr_t* const stack_frame_top = ContinuationHelper::InterpretedFrame::frame_top(f, callee_argsize, callee_interpreted);
1196   intptr_t* const stack_frame_bottom = ContinuationHelper::InterpretedFrame::frame_bottom(f);
1197   const int fsize = pointer_delta_as_int(stack_frame_bottom, stack_frame_top);
1198 
1199   DEBUG_ONLY(verify_frame_top(f, stack_frame_top));
1200 
1201   Method* frame_method = ContinuationHelper::Frame::frame_method(f);
1202   // including metadata between f and its args
1203   const int argsize = ContinuationHelper::InterpretedFrame::stack_argsize(f) + frame::metadata_words_at_top;
1204 
1205   log_develop_trace(continuations)("recurse_freeze_interpreted_frame %s _size: %d fsize: %d argsize: %d callee_interpreted: %d",
1206     frame_method->name_and_sig_as_C_string(), _freeze_size, fsize, argsize, callee_interpreted);
1207   // we'd rather not yield inside methods annotated with @JvmtiMountTransition
1208   assert(!ContinuationHelper::Frame::frame_method(f)->jvmti_mount_transition(), "");
1209 
1210   freeze_result result = recurse_freeze_java_frame<ContinuationHelper::InterpretedFrame>(f, caller, fsize, argsize);
1211   if (UNLIKELY(result > freeze_ok_bottom)) {
1212     return result;
1213   }
1214 
1215   bool is_bottom_frame = result == freeze_ok_bottom;
1216   assert(!caller.is_empty() || is_bottom_frame, "");
1217 
1218   DEBUG_ONLY(before_freeze_java_frame(f, caller, fsize, 0, is_bottom_frame);)
1219 
1220   frame hf = new_heap_frame<ContinuationHelper::InterpretedFrame>(f, caller);
1221   _total_align_size += frame::align_wiggle; // add alignment room for internal interpreted frame alignment on AArch64/PPC64
1222 
1223   intptr_t* heap_frame_top = ContinuationHelper::InterpretedFrame::frame_top(hf, callee_argsize, callee_interpreted);
1224   intptr_t* heap_frame_bottom = ContinuationHelper::InterpretedFrame::frame_bottom(hf);
1225   assert(heap_frame_bottom == heap_frame_top + fsize, "");
1226 
1227   // Some architectures (like AArch64/PPC64/RISC-V) add padding between the locals and the fixed_frame to keep the fp 16-byte-aligned.
1228   // On those architectures we freeze the padding in order to keep the same fp-relative offsets in the fixed_frame.
1229   copy_to_chunk(stack_frame_top, heap_frame_top, fsize);
1230   assert(!is_bottom_frame || !caller.is_interpreted_frame() || (heap_frame_top + fsize) == (caller.unextended_sp() + argsize), "");
1231 
1232   relativize_interpreted_frame_metadata(f, hf);
1233 
1234   patch(f, hf, caller, is_bottom_frame);
1235 
1236   CONT_JFR_ONLY(_jfr_info.record_interpreted_frame();)
1237   DEBUG_ONLY(after_freeze_java_frame(hf, is_bottom_frame);)
1238   caller = hf;
1239 
1240   // Mark frame_method's GC epoch for class redefinition on_stack calculation.
1241   frame_method->record_gc_epoch();
1242 
1243   return freeze_ok;
1244 }
1245 
1246 // The parameter callee_argsize includes metadata that has to be part of caller/callee overlap.
1247 // See also StackChunkFrameStream<frame_kind>::frame_size()
1248 freeze_result FreezeBase::recurse_freeze_compiled_frame(frame& f, frame& caller,
1249                                                         int callee_argsize /* incl. metadata */,
1250                                                         bool callee_interpreted) {
1251   // The frame's top never includes the stack arguments to the callee
1252   intptr_t* const stack_frame_top = ContinuationHelper::CompiledFrame::frame_top(f, callee_argsize, callee_interpreted);
1253   intptr_t* const stack_frame_bottom = ContinuationHelper::CompiledFrame::frame_bottom(f);
1254   // including metadata between f and its stackargs
1255   int argsize = ContinuationHelper::CompiledFrame::stack_argsize(f) + frame::metadata_words_at_top;
1256   int fsize = pointer_delta_as_int(stack_frame_bottom + argsize, stack_frame_top);
1257 
1258   int real_frame_size = 0;
1259   bool augmented = f.was_augmented_on_entry(real_frame_size);
1260   if (augmented) {
1261     // The args reside inside the frame so clear argsize. If the caller is compiled,
1262     // this will cause the stack arguments passed by the caller to be freezed when
1263     // freezing the caller frame itself. If the caller is interpreted this will have
1264     // the effect of discarding the arg area created in the i2c stub.
1265     argsize = 0;
1266     fsize = real_frame_size - (callee_interpreted ? 0 : callee_argsize);
1267 #ifdef ASSERT
1268     nmethod* nm = f.cb()->as_nmethod();
1269     Method* method = nm->method();
1270     address return_pc = ContinuationHelper::CompiledFrame::return_pc(f);
1271     CodeBlob* caller_cb = CodeCache::find_blob_fast(return_pc);
1272     assert(nm->is_compiled_by_c2() || (caller_cb->is_nmethod() && caller_cb->as_nmethod()->is_compiled_by_c2()), "caller or callee should be c2 compiled");
1273     assert((!caller_cb->is_nmethod() && nm->is_compiled_by_c2()) ||
1274            (nm->compiler_type() != caller_cb->as_nmethod()->compiler_type()) ||
1275            (nm->is_compiled_by_c2() && !method->is_static() && method->method_holder()->is_inline_klass()),
1276            "frame should not be extended");
1277 #endif
1278   }
1279 
1280   log_develop_trace(continuations)("recurse_freeze_compiled_frame %s _size: %d fsize: %d argsize: %d augmented: %d",
1281                              ContinuationHelper::Frame::frame_method(f) != nullptr ?
1282                              ContinuationHelper::Frame::frame_method(f)->name_and_sig_as_C_string() : "",
1283                              _freeze_size, fsize, argsize, augmented);
1284   // we'd rather not yield inside methods annotated with @JvmtiMountTransition
1285   assert(!ContinuationHelper::Frame::frame_method(f)->jvmti_mount_transition(), "");
1286 
1287   freeze_result result = recurse_freeze_java_frame<ContinuationHelper::CompiledFrame>(f, caller, fsize, argsize);
1288   if (UNLIKELY(result > freeze_ok_bottom)) {
1289     return result;
1290   }
1291 
1292   bool is_bottom_frame = result == freeze_ok_bottom;
1293   assert(!caller.is_empty() || is_bottom_frame, "");
1294   assert(!is_bottom_frame || !augmented, "thaw extended frame without caller?");
1295 
1296   DEBUG_ONLY(before_freeze_java_frame(f, caller, fsize, argsize, is_bottom_frame);)
1297 
1298   frame hf = new_heap_frame<ContinuationHelper::CompiledFrame>(f, caller, augmented ? real_frame_size - f.cb()->as_nmethod()->frame_size() : 0);
1299 
1300   intptr_t* heap_frame_top = ContinuationHelper::CompiledFrame::frame_top(hf, callee_argsize, callee_interpreted);
1301 
1302   copy_to_chunk(stack_frame_top, heap_frame_top, fsize);
1303   assert(!is_bottom_frame || !caller.is_compiled_frame() || (heap_frame_top + fsize) == (caller.unextended_sp() + argsize), "");
1304 
1305   if (caller.is_interpreted_frame()) {
1306     // When thawing the frame we might need to add alignment (see Thaw::align)
1307     _total_align_size += frame::align_wiggle;
1308   }
1309 
1310   patch(f, hf, caller, is_bottom_frame);
1311 
1312   assert(is_bottom_frame || Interpreter::contains(ContinuationHelper::CompiledFrame::real_pc(caller)) == caller.is_interpreted_frame(), "");
1313 
1314   DEBUG_ONLY(after_freeze_java_frame(hf, is_bottom_frame);)
1315   caller = hf;
1316   return freeze_ok;
1317 }
1318 
1319 NOINLINE freeze_result FreezeBase::recurse_freeze_stub_frame(frame& f, frame& caller) {
1320   DEBUG_ONLY(frame fsender = sender(f);)
1321   assert(fsender.is_compiled_frame(), "sender should be compiled frame");
1322 
1323   intptr_t* const stack_frame_top = ContinuationHelper::StubFrame::frame_top(f);
1324   const int fsize = f.cb()->frame_size();
1325 
1326   log_develop_trace(continuations)("recurse_freeze_stub_frame %s _size: %d fsize: %d :: " INTPTR_FORMAT " - " INTPTR_FORMAT,
1327     f.cb()->name(), _freeze_size, fsize, p2i(stack_frame_top), p2i(stack_frame_top+fsize));
1328 
1329   freeze_result result = recurse_freeze_java_frame<ContinuationHelper::StubFrame>(f, caller, fsize, 0);
1330   if (UNLIKELY(result > freeze_ok_bottom)) {
1331     return result;
1332   }
1333 
1334   assert(result == freeze_ok, "should have caller");
1335   DEBUG_ONLY(before_freeze_java_frame(f, caller, fsize, 0, false /*is_bottom_frame*/);)
1336 
1337   frame hf = new_heap_frame<ContinuationHelper::StubFrame>(f, caller);
1338   intptr_t* heap_frame_top = ContinuationHelper::StubFrame::frame_top(hf);
1339 
1340   copy_to_chunk(stack_frame_top, heap_frame_top, fsize);
1341 
1342   patch(f, hf, caller, false /*is_bottom_frame*/);
1343 
1344   DEBUG_ONLY(after_freeze_java_frame(hf, false /*is_bottom_frame*/);)
1345 
1346   caller = hf;
1347   return freeze_ok;
1348 }
1349 
1350 NOINLINE freeze_result FreezeBase::recurse_freeze_native_frame(frame& f, frame& caller) {
1351   if (!f.cb()->as_nmethod()->method()->is_object_wait0()) {
1352     assert(f.cb()->as_nmethod()->method()->is_synchronized(), "");
1353     // Synchronized native method case. Unlike the interpreter native wrapper, the compiled
1354     // native wrapper tries to acquire the monitor after marshalling the arguments from the
1355     // caller into the native convention. This is so that we have a valid oopMap in case of
1356     // having to block in the slow path. But that would require freezing those registers too
1357     // and then fixing them back on thaw in case of oops. To avoid complicating things and
1358     // given that this would be a rare case anyways just pin the vthread to the carrier.
1359     return freeze_pinned_native;
1360   }
1361 
1362   intptr_t* const stack_frame_top = ContinuationHelper::NativeFrame::frame_top(f);
1363   // There are no stackargs but argsize must include the metadata
1364   const int argsize = frame::metadata_words_at_top;
1365   const int fsize = f.cb()->frame_size() + argsize;
1366 
1367   log_develop_trace(continuations)("recurse_freeze_native_frame %s _size: %d fsize: %d :: " INTPTR_FORMAT " - " INTPTR_FORMAT,
1368     f.cb()->name(), _freeze_size, fsize, p2i(stack_frame_top), p2i(stack_frame_top+fsize));
1369 
1370   freeze_result result = recurse_freeze_java_frame<ContinuationHelper::NativeFrame>(f, caller, fsize, argsize);
1371   if (UNLIKELY(result > freeze_ok_bottom)) {
1372     return result;
1373   }
1374 
1375   assert(result == freeze_ok, "should have caller frame");
1376   DEBUG_ONLY(before_freeze_java_frame(f, caller, fsize, argsize, false /* is_bottom_frame */);)
1377 
1378   frame hf = new_heap_frame<ContinuationHelper::NativeFrame>(f, caller);
1379   intptr_t* heap_frame_top = ContinuationHelper::NativeFrame::frame_top(hf);
1380 
1381   copy_to_chunk(stack_frame_top, heap_frame_top, fsize);
1382 
1383   if (caller.is_interpreted_frame()) {
1384     // When thawing the frame we might need to add alignment (see Thaw::align)
1385     _total_align_size += frame::align_wiggle;
1386   }
1387 
1388   patch(f, hf, caller, false /* is_bottom_frame */);
1389 
1390   DEBUG_ONLY(after_freeze_java_frame(hf, false /* is_bottom_frame */);)
1391 
1392   caller = hf;
1393   return freeze_ok;
1394 }
1395 
1396 NOINLINE void FreezeBase::finish_freeze(const frame& f, const frame& top) {
1397   stackChunkOop chunk = _cont.tail();
1398 
1399   LogTarget(Trace, continuations) lt;
1400   if (lt.develop_is_enabled()) {
1401     LogStream ls(lt);
1402     assert(top.is_heap_frame(), "should be");
1403     top.print_on(&ls);
1404   }
1405 
1406   set_top_frame_metadata_pd(top);
1407 
1408   chunk->set_sp(chunk->to_offset(top.sp()));
1409   chunk->set_pc(top.pc());
1410 
1411   chunk->set_max_thawing_size(chunk->max_thawing_size() + _total_align_size);
1412 
1413   assert(chunk->sp_address() - chunk->start_address() >= _monitors_in_lockstack, "clash with lockstack");
1414 
1415   // At this point the chunk is consistent
1416 
1417   if (UNLIKELY(_barriers)) {
1418     log_develop_trace(continuations)("do barriers on old chunk");
1419     // Serial and Parallel GC can allocate objects directly into the old generation.
1420     // Then we want to relativize the derived pointers eagerly so that
1421     // old chunks are all in GC mode.
1422     assert(!UseG1GC, "G1 can not deal with allocating outside of eden");
1423     assert(!UseZGC, "ZGC can not deal with allocating chunks visible to marking");
1424     if (UseShenandoahGC) {
1425       _cont.tail()->relativize_derived_pointers_concurrently();
1426     } else {
1427       ContinuationGCSupport::transform_stack_chunk(_cont.tail());
1428     }
1429     // For objects in the old generation we must maintain the remembered set
1430     _cont.tail()->do_barriers<stackChunkOopDesc::BarrierType::Store>();
1431   }
1432 
1433   log_develop_trace(continuations)("finish_freeze: has_mixed_frames: %d", chunk->has_mixed_frames());
1434   if (lt.develop_is_enabled()) {
1435     LogStream ls(lt);
1436     chunk->print_on(true, &ls);
1437   }
1438 
1439   if (lt.develop_is_enabled()) {
1440     LogStream ls(lt);
1441     ls.print_cr("top hframe after (freeze):");
1442     assert(_cont.last_frame().is_heap_frame(), "should be");
1443     _cont.last_frame().print_on(&ls);
1444     DEBUG_ONLY(print_frame_layout(top, false, &ls);)
1445   }
1446 
1447   assert(_cont.chunk_invariant(), "");
1448 }
1449 
1450 inline bool FreezeBase::stack_overflow() { // detect stack overflow in recursive native code
1451   JavaThread* t = !_preempt ? _thread : JavaThread::current();
1452   assert(t == JavaThread::current(), "");
1453   if (os::current_stack_pointer() < t->stack_overflow_state()->shadow_zone_safe_limit()) {
1454     if (!_preempt) {
1455       ContinuationWrapper::SafepointOp so(t, _cont); // could also call _cont.done() instead
1456       Exceptions::_throw_msg(t, __FILE__, __LINE__, vmSymbols::java_lang_StackOverflowError(), "Stack overflow while freezing");
1457     }
1458     return true;
1459   }
1460   return false;
1461 }
1462 
1463 class StackChunkAllocator : public MemAllocator {
1464   const size_t                                 _stack_size;
1465   int                                          _argsize_md;
1466   ContinuationWrapper&                         _continuation_wrapper;
1467   JvmtiSampledObjectAllocEventCollector* const _jvmti_event_collector;
1468   mutable bool                                 _took_slow_path;
1469 
1470   // Does the minimal amount of initialization needed for a TLAB allocation.
1471   // We don't need to do a full initialization, as such an allocation need not be immediately walkable.
1472   virtual oop initialize(HeapWord* mem) const override {
1473     assert(_stack_size > 0, "");
1474     assert(_stack_size <= max_jint, "");
1475     assert(_word_size > _stack_size, "");
1476 
1477     // zero out fields (but not the stack)
1478     const size_t hs = oopDesc::header_size();
1479     if (oopDesc::has_klass_gap()) {
1480       oopDesc::set_klass_gap(mem, 0);
1481     }
1482     Copy::fill_to_aligned_words(mem + hs, vmClasses::StackChunk_klass()->size_helper() - hs);
1483 
1484     int bottom = (int)_stack_size - _argsize_md;
1485 
1486     jdk_internal_vm_StackChunk::set_size(mem, (int)_stack_size);
1487     jdk_internal_vm_StackChunk::set_bottom(mem, bottom);
1488     jdk_internal_vm_StackChunk::set_sp(mem, bottom);
1489 
1490     return finish(mem);
1491   }
1492 
1493   stackChunkOop allocate_fast() const {
1494     if (!UseTLAB) {
1495       return nullptr;
1496     }
1497 
1498     HeapWord* const mem = MemAllocator::mem_allocate_inside_tlab_fast();
1499     if (mem == nullptr) {
1500       return nullptr;
1501     }
1502 
1503     oop obj = initialize(mem);
1504     return stackChunkOopDesc::cast(obj);
1505   }
1506 
1507 public:
1508   StackChunkAllocator(Klass* klass,
1509                       size_t word_size,
1510                       Thread* thread,
1511                       size_t stack_size,
1512                       int argsize_md,
1513                       ContinuationWrapper& continuation_wrapper,
1514                       JvmtiSampledObjectAllocEventCollector* jvmti_event_collector)
1515     : MemAllocator(klass, word_size, thread),
1516       _stack_size(stack_size),
1517       _argsize_md(argsize_md),
1518       _continuation_wrapper(continuation_wrapper),
1519       _jvmti_event_collector(jvmti_event_collector),
1520       _took_slow_path(false) {}
1521 
1522   // Provides it's own, specialized allocation which skips instrumentation
1523   // if the memory can be allocated without going to a slow-path.
1524   stackChunkOop allocate() const {
1525     // First try to allocate without any slow-paths or instrumentation.
1526     stackChunkOop obj = allocate_fast();
1527     if (obj != nullptr) {
1528       return obj;
1529     }
1530 
1531     // Now try full-blown allocation with all expensive operations,
1532     // including potentially safepoint operations.
1533     _took_slow_path = true;
1534 
1535     // Protect unhandled Loom oops
1536     ContinuationWrapper::SafepointOp so(_thread, _continuation_wrapper);
1537 
1538     // Can safepoint
1539     _jvmti_event_collector->start();
1540 
1541     // Can safepoint
1542     return stackChunkOopDesc::cast(MemAllocator::allocate());
1543   }
1544 
1545   bool took_slow_path() const {
1546     return _took_slow_path;
1547   }
1548 };
1549 
1550 template <typename ConfigT>
1551 stackChunkOop Freeze<ConfigT>::allocate_chunk(size_t stack_size, int argsize_md) {
1552   log_develop_trace(continuations)("allocate_chunk allocating new chunk");
1553 
1554   InstanceStackChunkKlass* klass = InstanceStackChunkKlass::cast(vmClasses::StackChunk_klass());
1555   size_t size_in_words = klass->instance_size(stack_size);
1556 
1557   if (CollectedHeap::stack_chunk_max_size() > 0 && size_in_words >= CollectedHeap::stack_chunk_max_size()) {
1558     if (!_preempt) {
1559       throw_stack_overflow_on_humongous_chunk();
1560     }
1561     return nullptr;
1562   }
1563 
1564   JavaThread* current = _preempt ? JavaThread::current() : _thread;
1565   assert(current == JavaThread::current(), "should be current");
1566 
1567   // Allocate the chunk.
1568   //
1569   // This might safepoint while allocating, but all safepointing due to
1570   // instrumentation have been deferred. This property is important for
1571   // some GCs, as this ensures that the allocated object is in the young
1572   // generation / newly allocated memory.
1573   StackChunkAllocator allocator(klass, size_in_words, current, stack_size, argsize_md, _cont, _jvmti_event_collector);
1574   stackChunkOop chunk = allocator.allocate();
1575 
1576   if (chunk == nullptr) {
1577     return nullptr; // OOME
1578   }
1579 
1580   // assert that chunk is properly initialized
1581   assert(chunk->stack_size() == (int)stack_size, "");
1582   assert(chunk->size() >= stack_size, "chunk->size(): %zu size: %zu", chunk->size(), stack_size);
1583   assert(chunk->sp() == chunk->bottom(), "");
1584   assert((intptr_t)chunk->start_address() % 8 == 0, "");
1585   assert(chunk->max_thawing_size() == 0, "");
1586   assert(chunk->pc() == nullptr, "");
1587   assert(chunk->is_empty(), "");
1588   assert(chunk->flags() == 0, "");
1589   assert(chunk->is_gc_mode() == false, "");
1590   assert(chunk->lockstack_size() == 0, "");
1591 
1592   // fields are uninitialized
1593   chunk->set_parent_access<IS_DEST_UNINITIALIZED>(_cont.last_nonempty_chunk());
1594   chunk->set_cont_access<IS_DEST_UNINITIALIZED>(_cont.continuation());
1595 
1596 #if INCLUDE_ZGC
1597   if (UseZGC) {
1598     ZStackChunkGCData::initialize(chunk);
1599     assert(!chunk->requires_barriers(), "ZGC always allocates in the young generation");
1600     _barriers = false;
1601   } else
1602 #endif
1603 #if INCLUDE_SHENANDOAHGC
1604   if (UseShenandoahGC) {
1605     _barriers = chunk->requires_barriers();
1606   } else
1607 #endif
1608   {
1609     if (!allocator.took_slow_path()) {
1610       // Guaranteed to be in young gen / newly allocated memory
1611       assert(!chunk->requires_barriers(), "Unfamiliar GC requires barriers on TLAB allocation");
1612       _barriers = false;
1613     } else {
1614       // Some GCs could put direct allocations in old gen for slow-path
1615       // allocations; need to explicitly check if that was the case.
1616       _barriers = chunk->requires_barriers();
1617     }
1618   }
1619 
1620   if (_barriers) {
1621     log_develop_trace(continuations)("allocation requires barriers");
1622   }
1623 
1624   assert(chunk->parent() == nullptr || chunk->parent()->is_stackChunk(), "");
1625 
1626   return chunk;
1627 }
1628 
1629 void FreezeBase::throw_stack_overflow_on_humongous_chunk() {
1630   ContinuationWrapper::SafepointOp so(_thread, _cont); // could also call _cont.done() instead
1631   Exceptions::_throw_msg(_thread, __FILE__, __LINE__, vmSymbols::java_lang_StackOverflowError(), "Humongous stack chunk");
1632 }
1633 
1634 #if INCLUDE_JVMTI
1635 static int num_java_frames(ContinuationWrapper& cont) {
1636   ResourceMark rm; // used for scope traversal in num_java_frames(nmethod*, address)
1637   int count = 0;
1638   for (stackChunkOop chunk = cont.tail(); chunk != nullptr; chunk = chunk->parent()) {
1639     count += chunk->num_java_frames();
1640   }
1641   return count;
1642 }
1643 
1644 static void invalidate_jvmti_stack(JavaThread* thread) {
1645   JvmtiThreadState *state = thread->jvmti_thread_state();
1646   if (state != nullptr) {
1647     state->invalidate_cur_stack_depth();
1648   }
1649 }
1650 
1651 static void jvmti_yield_cleanup(JavaThread* thread, ContinuationWrapper& cont) {
1652   if (JvmtiExport::has_frame_pops(thread)) {
1653     int num_frames = num_java_frames(cont);
1654 
1655     ContinuationWrapper::SafepointOp so(Thread::current(), cont);
1656     JvmtiExport::continuation_yield_cleanup(JavaThread::current(), num_frames);
1657   }
1658   invalidate_jvmti_stack(thread);
1659 }
1660 
1661 static void jvmti_mount_end(JavaThread* current, ContinuationWrapper& cont, frame top) {
1662   assert(current->vthread() != nullptr, "must be");
1663 
1664   HandleMarkCleaner hm(current);
1665   Handle vth(current, current->vthread());
1666 
1667   ContinuationWrapper::SafepointOp so(current, cont);
1668 
1669   // Since we might safepoint set the anchor so that the stack can be walked.
1670   set_anchor(current, top.sp());
1671 
1672   JRT_BLOCK
1673     JvmtiVTMSTransitionDisabler::VTMS_vthread_mount((jthread)vth.raw_value(), false);
1674 
1675     if (current->pending_contended_entered_event()) {
1676       JvmtiExport::post_monitor_contended_entered(current, current->contended_entered_monitor());
1677       current->set_contended_entered_monitor(nullptr);
1678     }
1679   JRT_BLOCK_END
1680 
1681   clear_anchor(current);
1682 }
1683 #endif // INCLUDE_JVMTI
1684 
1685 #ifdef ASSERT
1686 // There are no interpreted frames if we're not called from the interpreter and we haven't ancountered an i2c
1687 // adapter or called Deoptimization::unpack_frames. As for native frames, upcalls from JNI also go through the
1688 // interpreter (see JavaCalls::call_helper), while the UpcallLinker explicitly sets cont_fastpath.
1689 bool FreezeBase::check_valid_fast_path() {
1690   ContinuationEntry* ce = _thread->last_continuation();
1691   RegisterMap map(_thread,
1692                   RegisterMap::UpdateMap::skip,
1693                   RegisterMap::ProcessFrames::skip,
1694                   RegisterMap::WalkContinuation::skip);
1695   map.set_include_argument_oops(false);
1696   bool is_top_frame = true;
1697   for (frame f = freeze_start_frame(); Continuation::is_frame_in_continuation(ce, f); f = f.sender(&map), is_top_frame = false) {
1698     if (!((f.is_compiled_frame() && !f.is_deoptimized_frame()) || (is_top_frame && (f.is_runtime_frame() || f.is_native_frame())))) {
1699       return false;
1700     }
1701   }
1702   return true;
1703 }
1704 #endif // ASSERT
1705 
1706 static inline freeze_result freeze_epilog(ContinuationWrapper& cont) {
1707   verify_continuation(cont.continuation());
1708   assert(!cont.is_empty(), "");
1709 
1710   log_develop_debug(continuations)("=== End of freeze cont ### #" INTPTR_FORMAT, cont.hash());
1711   return freeze_ok;
1712 }
1713 
1714 static freeze_result freeze_epilog(JavaThread* thread, ContinuationWrapper& cont, freeze_result res) {
1715   if (UNLIKELY(res != freeze_ok)) {
1716     JFR_ONLY(thread->set_last_freeze_fail_result(res);)
1717     verify_continuation(cont.continuation());
1718     log_develop_trace(continuations)("=== end of freeze (fail %d)", res);
1719     return res;
1720   }
1721 
1722   JVMTI_ONLY(jvmti_yield_cleanup(thread, cont)); // can safepoint
1723   return freeze_epilog(cont);
1724 }
1725 
1726 static freeze_result preempt_epilog(ContinuationWrapper& cont, freeze_result res, frame& old_last_frame) {
1727   if (UNLIKELY(res != freeze_ok)) {
1728     verify_continuation(cont.continuation());
1729     log_develop_trace(continuations)("=== end of freeze (fail %d)", res);
1730     return res;
1731   }
1732 
1733   patch_return_pc_with_preempt_stub(old_last_frame);
1734   cont.tail()->set_preempted(true);
1735 
1736   return freeze_epilog(cont);
1737 }
1738 
1739 template<typename ConfigT, bool preempt>
1740 static inline freeze_result freeze_internal(JavaThread* current, intptr_t* const sp) {
1741   assert(!current->has_pending_exception(), "");
1742 
1743 #ifdef ASSERT
1744   log_trace(continuations)("~~~~ freeze sp: " INTPTR_FORMAT "JavaThread: " INTPTR_FORMAT, p2i(current->last_continuation()->entry_sp()), p2i(current));
1745   log_frames(current);
1746 #endif
1747 
1748   CONT_JFR_ONLY(EventContinuationFreeze event;)
1749 
1750   ContinuationEntry* entry = current->last_continuation();
1751 
1752   oop oopCont = entry->cont_oop(current);
1753   assert(oopCont == current->last_continuation()->cont_oop(current), "");
1754   assert(ContinuationEntry::assert_entry_frame_laid_out(current), "");
1755 
1756   verify_continuation(oopCont);
1757   ContinuationWrapper cont(current, oopCont);
1758   log_develop_debug(continuations)("FREEZE #" INTPTR_FORMAT " " INTPTR_FORMAT, cont.hash(), p2i((oopDesc*)oopCont));
1759 
1760   assert(entry->is_virtual_thread() == (entry->scope(current) == java_lang_VirtualThread::vthread_scope()), "");
1761 
1762   if (entry->is_pinned()) {
1763     log_develop_debug(continuations)("PINNED due to critical section");
1764     verify_continuation(cont.continuation());
1765     const freeze_result res = freeze_pinned_cs;
1766     if (!preempt) {
1767       JFR_ONLY(current->set_last_freeze_fail_result(res);)
1768     }
1769     log_develop_trace(continuations)("=== end of freeze (fail %d)", res);
1770     // Avoid Thread.yield() loops without safepoint polls.
1771     if (SafepointMechanism::should_process(current) && !preempt) {
1772       cont.done(); // allow safepoint
1773       ThreadInVMfromJava tivmfj(current);
1774     }
1775     return res;
1776   }
1777 
1778   Freeze<ConfigT> freeze(current, cont, sp, preempt);
1779 
1780   assert(!current->cont_fastpath() || freeze.check_valid_fast_path(), "");
1781   bool fast = UseContinuationFastPath && current->cont_fastpath();
1782   if (fast && freeze.size_if_fast_freeze_available() > 0) {
1783     freeze.freeze_fast_existing_chunk();
1784     CONT_JFR_ONLY(freeze.jfr_info().post_jfr_event(&event, oopCont, current);)
1785     return !preempt ? freeze_epilog(cont) : preempt_epilog(cont, freeze_ok, freeze.last_frame());
1786   }
1787 
1788   if (preempt) {
1789     JvmtiSampledObjectAllocEventCollector jsoaec(false);
1790     freeze.set_jvmti_event_collector(&jsoaec);
1791 
1792     freeze_result res = fast ? freeze.try_freeze_fast() : freeze.freeze_slow();
1793 
1794     CONT_JFR_ONLY(freeze.jfr_info().post_jfr_event(&event, oopCont, current);)
1795     preempt_epilog(cont, res, freeze.last_frame());
1796     return res;
1797   }
1798 
1799   log_develop_trace(continuations)("chunk unavailable; transitioning to VM");
1800   assert(current == JavaThread::current(), "must be current thread");
1801   JRT_BLOCK
1802     // delays a possible JvmtiSampledObjectAllocEventCollector in alloc_chunk
1803     JvmtiSampledObjectAllocEventCollector jsoaec(false);
1804     freeze.set_jvmti_event_collector(&jsoaec);
1805 
1806     freeze_result res = fast ? freeze.try_freeze_fast() : freeze.freeze_slow();
1807 
1808     CONT_JFR_ONLY(freeze.jfr_info().post_jfr_event(&event, oopCont, current);)
1809     freeze_epilog(current, cont, res);
1810     cont.done(); // allow safepoint in the transition back to Java
1811     return res;
1812   JRT_BLOCK_END
1813 }
1814 
1815 static freeze_result is_pinned0(JavaThread* thread, oop cont_scope, bool safepoint) {
1816   ContinuationEntry* entry = thread->last_continuation();
1817   if (entry == nullptr) {
1818     return freeze_ok;
1819   }
1820   if (entry->is_pinned()) {
1821     return freeze_pinned_cs;
1822   }
1823 
1824   RegisterMap map(thread,
1825                   RegisterMap::UpdateMap::include,
1826                   RegisterMap::ProcessFrames::skip,
1827                   RegisterMap::WalkContinuation::skip);
1828   map.set_include_argument_oops(false);
1829   frame f = thread->last_frame();
1830 
1831   if (!safepoint) {
1832     f = f.sender(&map); // this is the yield frame
1833   } else { // safepoint yield
1834 #if (defined(X86) || defined(AARCH64) || defined(RISCV64)) && !defined(ZERO)
1835     f.set_fp(f.real_fp()); // Instead of this, maybe in ContinuationWrapper::set_last_frame always use the real_fp?
1836 #else
1837     Unimplemented();
1838 #endif
1839     if (!Interpreter::contains(f.pc())) {
1840       assert(ContinuationHelper::Frame::is_stub(f.cb()), "must be");
1841       assert(f.oop_map() != nullptr, "must be");
1842       f.oop_map()->update_register_map(&f, &map); // we have callee-save registers in this case
1843     }
1844   }
1845 
1846   while (true) {
1847     if ((f.is_interpreted_frame() && f.interpreter_frame_method()->is_native()) || f.is_native_frame()) {
1848       return freeze_pinned_native;
1849     }
1850 
1851     f = f.sender(&map);
1852     if (!Continuation::is_frame_in_continuation(entry, f)) {
1853       oop scope = jdk_internal_vm_Continuation::scope(entry->cont_oop(thread));
1854       if (scope == cont_scope) {
1855         break;
1856       }
1857       entry = entry->parent();
1858       if (entry == nullptr) {
1859         break;
1860       }
1861       if (entry->is_pinned()) {
1862         return freeze_pinned_cs;
1863       }
1864     }
1865   }
1866   return freeze_ok;
1867 }
1868 
1869 /////////////// THAW ////
1870 
1871 static int thaw_size(stackChunkOop chunk) {
1872   int size = chunk->max_thawing_size();
1873   size += frame::metadata_words; // For the top pc+fp in push_return_frame or top = stack_sp - frame::metadata_words in thaw_fast
1874   size += 2*frame::align_wiggle; // in case of alignments at the top and bottom
1875   return size;
1876 }
1877 
1878 // make room on the stack for thaw
1879 // returns the size in bytes, or 0 on failure
1880 static inline int prepare_thaw_internal(JavaThread* thread, bool return_barrier) {
1881   log_develop_trace(continuations)("~~~~ prepare_thaw return_barrier: %d", return_barrier);
1882 
1883   assert(thread == JavaThread::current(), "");
1884 
1885   ContinuationEntry* ce = thread->last_continuation();
1886   assert(ce != nullptr, "");
1887   oop continuation = ce->cont_oop(thread);
1888   assert(continuation == get_continuation(thread), "");
1889   verify_continuation(continuation);
1890 
1891   stackChunkOop chunk = jdk_internal_vm_Continuation::tail(continuation);
1892   assert(chunk != nullptr, "");
1893 
1894   // The tail can be empty because it might still be available for another freeze.
1895   // However, here we want to thaw, so we get rid of it (it will be GCed).
1896   if (UNLIKELY(chunk->is_empty())) {
1897     chunk = chunk->parent();
1898     assert(chunk != nullptr, "");
1899     assert(!chunk->is_empty(), "");
1900     jdk_internal_vm_Continuation::set_tail(continuation, chunk);
1901   }
1902 
1903   // Verification
1904   chunk->verify();
1905   assert(chunk->max_thawing_size() > 0, "chunk invariant violated; expected to not be empty");
1906 
1907   // Only make space for the last chunk because we only thaw from the last chunk
1908   int size = thaw_size(chunk) << LogBytesPerWord;
1909 
1910   const address bottom = (address)thread->last_continuation()->entry_sp();
1911   // 300 is an estimate for stack size taken for this native code, in addition to StackShadowPages
1912   // for the Java frames in the check below.
1913   if (!stack_overflow_check(thread, size + 300, bottom)) {
1914     return 0;
1915   }
1916 
1917   log_develop_trace(continuations)("prepare_thaw bottom: " INTPTR_FORMAT " top: " INTPTR_FORMAT " size: %d",
1918                               p2i(bottom), p2i(bottom - size), size);
1919   return size;
1920 }
1921 
1922 class ThawBase : public StackObj {
1923 protected:
1924   JavaThread* _thread;
1925   ContinuationWrapper& _cont;
1926   CONT_JFR_ONLY(FreezeThawJfrInfo _jfr_info;)
1927 
1928   intptr_t* _fastpath;
1929   bool _barriers;
1930   bool _preempted_case;
1931   intptr_t* _top_unextended_sp_before_thaw;
1932   int _align_size;
1933   DEBUG_ONLY(intptr_t* _top_stack_address);
1934 
1935   StackChunkFrameStream<ChunkFrames::Mixed> _stream;
1936 
1937   NOT_PRODUCT(int _frames;)
1938 
1939 protected:
1940   ThawBase(JavaThread* thread, ContinuationWrapper& cont) :
1941       _thread(thread), _cont(cont),
1942       _fastpath(nullptr) {
1943     DEBUG_ONLY(_top_unextended_sp_before_thaw = nullptr;)
1944     assert (cont.tail() != nullptr, "no last chunk");
1945     DEBUG_ONLY(_top_stack_address = _cont.entrySP() - thaw_size(cont.tail());)
1946   }
1947 
1948   void clear_chunk(stackChunkOop chunk);
1949   template<bool check_stub>
1950   int remove_top_compiled_frame_from_chunk(stackChunkOop chunk, int &argsize);
1951   int remove_scalarized_frames(StackChunkFrameStream<ChunkFrames::CompiledOnly>& scfs, int &argsize);
1952   void copy_from_chunk(intptr_t* from, intptr_t* to, int size);
1953 
1954   void thaw_lockstack(stackChunkOop chunk);
1955 
1956   // fast path
1957   inline void prefetch_chunk_pd(void* start, int size_words);
1958   void patch_return(intptr_t* sp, bool is_last);
1959 
1960   intptr_t* handle_preempted_continuation(intptr_t* sp, Continuation::preempt_kind preempt_kind, bool fast_case);
1961   inline intptr_t* push_cleanup_continuation();
1962   void throw_interrupted_exception(JavaThread* current, frame& top);
1963 
1964   void recurse_thaw(const frame& heap_frame, frame& caller, int num_frames, bool top_on_preempt_case);
1965   void finish_thaw(frame& f);
1966 
1967 private:
1968   template<typename FKind> bool recurse_thaw_java_frame(frame& caller, int num_frames);
1969   void finalize_thaw(frame& entry, int argsize);
1970 
1971   inline bool seen_by_gc();
1972 
1973   inline void before_thaw_java_frame(const frame& hf, const frame& caller, bool bottom, int num_frame);
1974   inline void after_thaw_java_frame(const frame& f, bool bottom);
1975   inline void patch(frame& f, const frame& caller, bool bottom, bool augmented = false);
1976   void clear_bitmap_bits(address start, address end);
1977 
1978   NOINLINE void recurse_thaw_interpreted_frame(const frame& hf, frame& caller, int num_frames);
1979   void recurse_thaw_compiled_frame(const frame& hf, frame& caller, int num_frames, bool stub_caller);
1980   void recurse_thaw_stub_frame(const frame& hf, frame& caller, int num_frames);
1981   void recurse_thaw_native_frame(const frame& hf, frame& caller, int num_frames);
1982 
1983   void push_return_frame(frame& f);
1984   inline frame new_entry_frame();
1985   template<typename FKind> frame new_stack_frame(const frame& hf, frame& caller, bool bottom, int size_adjust = 0);
1986   inline void patch_pd(frame& f, const frame& sender);
1987   inline void patch_pd(frame& f, intptr_t* caller_sp);
1988   inline intptr_t* align(const frame& hf, intptr_t* frame_sp, frame& caller, bool bottom);
1989 
1990   void maybe_set_fastpath(intptr_t* sp) { if (sp > _fastpath) _fastpath = sp; }
1991 
1992   static inline void derelativize_interpreted_frame_metadata(const frame& hf, const frame& f);
1993 
1994  public:
1995   CONT_JFR_ONLY(FreezeThawJfrInfo& jfr_info() { return _jfr_info; })
1996 };
1997 
1998 template <typename ConfigT>
1999 class Thaw : public ThawBase {
2000 public:
2001   Thaw(JavaThread* thread, ContinuationWrapper& cont) : ThawBase(thread, cont) {}
2002 
2003   inline bool can_thaw_fast(stackChunkOop chunk) {
2004     return    !_barriers
2005            &&  _thread->cont_fastpath_thread_state()
2006            && !chunk->has_thaw_slowpath_condition()
2007            && !PreserveFramePointer;
2008   }
2009 
2010   inline intptr_t* thaw(Continuation::thaw_kind kind);
2011   template<bool check_stub = false>
2012   NOINLINE intptr_t* thaw_fast(stackChunkOop chunk);
2013   NOINLINE intptr_t* thaw_slow(stackChunkOop chunk, Continuation::thaw_kind kind);
2014   inline void patch_caller_links(intptr_t* sp, intptr_t* bottom);
2015 };
2016 
2017 template <typename ConfigT>
2018 inline intptr_t* Thaw<ConfigT>::thaw(Continuation::thaw_kind kind) {
2019   verify_continuation(_cont.continuation());
2020   assert(!jdk_internal_vm_Continuation::done(_cont.continuation()), "");
2021   assert(!_cont.is_empty(), "");
2022 
2023   stackChunkOop chunk = _cont.tail();
2024   assert(chunk != nullptr, "guaranteed by prepare_thaw");
2025   assert(!chunk->is_empty(), "guaranteed by prepare_thaw");
2026 
2027   _barriers = chunk->requires_barriers();
2028   return (LIKELY(can_thaw_fast(chunk))) ? thaw_fast(chunk)
2029                                         : thaw_slow(chunk, kind);
2030 }
2031 
2032 class ReconstructedStack : public StackObj {
2033   intptr_t* _base;  // _cont.entrySP(); // top of the entry frame
2034   int _thaw_size;
2035   int _argsize;
2036 public:
2037   ReconstructedStack(intptr_t* base, int thaw_size, int argsize)
2038   : _base(base), _thaw_size(thaw_size - (argsize == 0 ? frame::metadata_words_at_top : 0)), _argsize(argsize) {
2039     // The only possible source of misalignment is stack-passed arguments b/c compiled frames are 16-byte aligned.
2040     assert(argsize != 0 || (_base - _thaw_size) == ContinuationHelper::frame_align_pointer(_base - _thaw_size), "");
2041     // We're at most one alignment word away from entrySP
2042     assert(_base - 1 <= top() + total_size() + frame::metadata_words_at_bottom, "missed entry frame");
2043   }
2044 
2045   int entry_frame_extension() const { return _argsize + (_argsize > 0 ? frame::metadata_words_at_top : 0); }
2046 
2047   // top and bottom stack pointers
2048   intptr_t* sp() const { return ContinuationHelper::frame_align_pointer(_base - _thaw_size); }
2049   intptr_t* bottom_sp() const { return ContinuationHelper::frame_align_pointer(_base - entry_frame_extension()); }
2050 
2051   // several operations operate on the totality of the stack being reconstructed,
2052   // including the metadata words
2053   intptr_t* top() const { return sp() - frame::metadata_words_at_bottom;  }
2054   int total_size() const { return _thaw_size + frame::metadata_words_at_bottom; }
2055 };
2056 
2057 inline void ThawBase::clear_chunk(stackChunkOop chunk) {
2058   chunk->set_sp(chunk->bottom());
2059   chunk->set_max_thawing_size(0);
2060 }
2061 
2062 int ThawBase::remove_scalarized_frames(StackChunkFrameStream<ChunkFrames::CompiledOnly>& f, int &argsize) {
2063   intptr_t* top = f.sp();
2064 
2065   while (f.cb()->as_nmethod()->needs_stack_repair()) {
2066     f.next(SmallRegisterMap::instance(), false /* stop */);
2067   }
2068   assert(!f.is_done(), "");
2069   assert(f.is_compiled(), "");
2070 
2071   intptr_t* bottom = f.sp() + f.cb()->frame_size();
2072   argsize = f.stack_argsize();
2073   return bottom - top;
2074 }
2075 
2076 template<bool check_stub>
2077 int ThawBase::remove_top_compiled_frame_from_chunk(stackChunkOop chunk, int &argsize) {
2078   bool empty = false;
2079   StackChunkFrameStream<ChunkFrames::CompiledOnly> f(chunk);
2080   DEBUG_ONLY(intptr_t* const chunk_sp = chunk->start_address() + chunk->sp();)
2081   assert(chunk_sp == f.sp(), "");
2082   assert(chunk_sp == f.unextended_sp(), "");
2083 
2084   int frame_size = f.cb()->frame_size();
2085   argsize = f.stack_argsize();
2086 
2087   assert(!f.is_stub() || check_stub, "");
2088   if (check_stub && f.is_stub()) {
2089     // If we don't thaw the top compiled frame too, after restoring the saved
2090     // registers back in Java, we would hit the return barrier to thaw one more
2091     // frame effectively overwriting the restored registers during that call.
2092     f.next(SmallRegisterMap::instance(), true /* stop */);
2093     assert(!f.is_done(), "");
2094 
2095     f.get_cb();
2096     assert(f.is_compiled(), "");
2097     if (f.cb()->as_nmethod()->is_marked_for_deoptimization()) {
2098       // The caller of the runtime stub when the continuation is preempted is not at a
2099       // Java call instruction, and so cannot rely on nmethod patching for deopt.
2100       log_develop_trace(continuations)("Deoptimizing runtime stub caller");
2101       f.to_frame().deoptimize(nullptr); // the null thread simply avoids the assertion in deoptimize which we're not set up for
2102     }
2103 
2104     if (f.cb()->as_nmethod()->needs_stack_repair()) {
2105       frame_size += remove_scalarized_frames(f, argsize);
2106     } else {
2107       frame_size += f.cb()->frame_size();
2108       argsize = f.stack_argsize();
2109     }
2110   } else if (f.cb()->as_nmethod()->needs_stack_repair()) {
2111     frame_size = remove_scalarized_frames(f, argsize);
2112   }
2113 
2114   f.next(SmallRegisterMap::instance(), true /* stop */);
2115   empty = f.is_done();
2116   assert(!empty || argsize == chunk->argsize(), "");
2117 
2118   if (empty) {
2119     clear_chunk(chunk);
2120   } else {
2121     chunk->set_sp(chunk->sp() + frame_size);
2122     chunk->set_max_thawing_size(chunk->max_thawing_size() - frame_size);
2123     // We set chunk->pc to the return pc into the next frame
2124     chunk->set_pc(f.pc());
2125 #ifdef ASSERT
2126     {
2127       intptr_t* retaddr_slot = (chunk_sp
2128                                 + frame_size
2129                                 - frame::sender_sp_ret_address_offset());
2130       assert(f.pc() == ContinuationHelper::return_address_at(retaddr_slot),
2131              "unexpected pc");
2132     }
2133 #endif
2134   }
2135   assert(empty == chunk->is_empty(), "");
2136   // returns the size required to store the frame on stack, and because it is a
2137   // compiled frame, it must include a copy of the arguments passed by the caller
2138   return frame_size + argsize + frame::metadata_words_at_top;
2139 }
2140 
2141 void ThawBase::thaw_lockstack(stackChunkOop chunk) {
2142   int lockStackSize = chunk->lockstack_size();
2143   assert(lockStackSize > 0 && lockStackSize <= LockStack::CAPACITY, "");
2144 
2145   oop tmp_lockstack[LockStack::CAPACITY];
2146   chunk->transfer_lockstack(tmp_lockstack, _barriers);
2147   _thread->lock_stack().move_from_address(tmp_lockstack, lockStackSize);
2148 
2149   chunk->set_lockstack_size(0);
2150   chunk->set_has_lockstack(false);
2151 }
2152 
2153 void ThawBase::copy_from_chunk(intptr_t* from, intptr_t* to, int size) {
2154   assert(to >= _top_stack_address, "overwrote past thawing space"
2155     " to: " INTPTR_FORMAT " top_address: " INTPTR_FORMAT, p2i(to), p2i(_top_stack_address));
2156   assert(to + size <= _cont.entrySP(), "overwrote past thawing space");
2157   _cont.tail()->copy_from_chunk_to_stack(from, to, size);
2158   CONT_JFR_ONLY(_jfr_info.record_size_copied(size);)
2159 }
2160 
2161 void ThawBase::patch_return(intptr_t* sp, bool is_last) {
2162   log_develop_trace(continuations)("thaw_fast patching -- sp: " INTPTR_FORMAT, p2i(sp));
2163 
2164   address pc = !is_last ? StubRoutines::cont_returnBarrier() : _cont.entryPC();
2165   ContinuationHelper::patch_return_address_at(
2166     sp - frame::sender_sp_ret_address_offset(),
2167     pc);
2168 }
2169 
2170 template <typename ConfigT>
2171 template<bool check_stub>
2172 NOINLINE intptr_t* Thaw<ConfigT>::thaw_fast(stackChunkOop chunk) {
2173   assert(chunk == _cont.tail(), "");
2174   assert(!chunk->has_mixed_frames(), "");
2175   assert(!chunk->requires_barriers(), "");
2176   assert(!chunk->has_bitmap(), "");
2177   assert(!_thread->is_interp_only_mode(), "");
2178 
2179   LogTarget(Trace, continuations) lt;
2180   if (lt.develop_is_enabled()) {
2181     LogStream ls(lt);
2182     ls.print_cr("thaw_fast");
2183     chunk->print_on(true, &ls);
2184   }
2185 
2186   // Below this heuristic, we thaw the whole chunk, above it we thaw just one frame.
2187   static const int threshold = 500; // words
2188 
2189   const int full_chunk_size = chunk->stack_size() - chunk->sp(); // this initial size could be reduced if it's a partial thaw
2190   int argsize, thaw_size;
2191 
2192   intptr_t* const chunk_sp = chunk->start_address() + chunk->sp();
2193 
2194   bool partial, empty;
2195   if (LIKELY(!TEST_THAW_ONE_CHUNK_FRAME && (full_chunk_size < threshold))) {
2196     prefetch_chunk_pd(chunk->start_address(), full_chunk_size); // prefetch anticipating memcpy starting at highest address
2197 
2198     partial = false;
2199     argsize = chunk->argsize(); // must be called *before* clearing the chunk
2200     clear_chunk(chunk);
2201     thaw_size = full_chunk_size;
2202     empty = true;
2203   } else { // thaw a single frame
2204     partial = true;
2205     thaw_size = remove_top_compiled_frame_from_chunk<check_stub>(chunk, argsize);
2206     empty = chunk->is_empty();
2207   }
2208 
2209   // Are we thawing the last frame(s) in the continuation
2210   const bool is_last = empty && chunk->parent() == nullptr;
2211   assert(!is_last || argsize == 0, "");
2212 
2213   log_develop_trace(continuations)("thaw_fast partial: %d is_last: %d empty: %d size: %d argsize: %d entrySP: " PTR_FORMAT,
2214                               partial, is_last, empty, thaw_size, argsize, p2i(_cont.entrySP()));
2215 
2216   ReconstructedStack rs(_cont.entrySP(), thaw_size, argsize);
2217 
2218   // also copy metadata words at frame bottom
2219   copy_from_chunk(chunk_sp - frame::metadata_words_at_bottom, rs.top(), rs.total_size());
2220 
2221   // update the ContinuationEntry
2222   _cont.set_argsize(argsize);
2223   log_develop_trace(continuations)("setting entry argsize: %d", _cont.argsize());
2224   assert(rs.bottom_sp() == _cont.entry()->bottom_sender_sp(), "");
2225 
2226   // install the return barrier if not last frame, or the entry's pc if last
2227   patch_return(rs.bottom_sp(), is_last);
2228 
2229   // insert the back links from callee to caller frames
2230   patch_caller_links(rs.top(), rs.top() + rs.total_size());
2231 
2232   assert(is_last == _cont.is_empty(), "");
2233   assert(_cont.chunk_invariant(), "");
2234 
2235 #if CONT_JFR
2236   EventContinuationThawFast e;
2237   if (e.should_commit()) {
2238     e.set_id(cast_from_oop<u8>(chunk));
2239     e.set_size(thaw_size << LogBytesPerWord);
2240     e.set_full(!partial);
2241     e.commit();
2242   }
2243 #endif
2244 
2245 #ifdef ASSERT
2246   set_anchor(_thread, rs.sp());
2247   log_frames(_thread);
2248   if (LoomDeoptAfterThaw) {
2249     do_deopt_after_thaw(_thread);
2250   }
2251   clear_anchor(_thread);
2252 #endif
2253 
2254   return rs.sp();
2255 }
2256 
2257 inline bool ThawBase::seen_by_gc() {
2258   return _barriers || _cont.tail()->is_gc_mode();
2259 }
2260 
2261 static inline void relativize_chunk_concurrently(stackChunkOop chunk) {
2262 #if INCLUDE_ZGC || INCLUDE_SHENANDOAHGC
2263   if (UseZGC || UseShenandoahGC) {
2264     chunk->relativize_derived_pointers_concurrently();
2265   }
2266 #endif
2267 }
2268 
2269 template <typename ConfigT>
2270 NOINLINE intptr_t* Thaw<ConfigT>::thaw_slow(stackChunkOop chunk, Continuation::thaw_kind kind) {
2271   Continuation::preempt_kind preempt_kind;
2272   bool retry_fast_path = false;
2273 
2274   _preempted_case = chunk->preempted();
2275   if (_preempted_case) {
2276     ObjectWaiter* waiter = java_lang_VirtualThread::objectWaiter(_thread->vthread());
2277     if (waiter != nullptr) {
2278       // Mounted again after preemption. Resume the pending monitor operation,
2279       // which will be either a monitorenter or Object.wait() call.
2280       ObjectMonitor* mon = waiter->monitor();
2281       preempt_kind = waiter->is_wait() ? Continuation::freeze_on_wait : Continuation::freeze_on_monitorenter;
2282 
2283       bool mon_acquired = mon->resume_operation(_thread, waiter, _cont);
2284       assert(!mon_acquired || mon->has_owner(_thread), "invariant");
2285       if (!mon_acquired) {
2286         // Failed to acquire monitor. Return to enterSpecial to unmount again.
2287         return push_cleanup_continuation();
2288       }
2289       chunk = _cont.tail();  // reload oop in case of safepoint in resume_operation (if posting JVMTI events).
2290     } else {
2291       // Preemption cancelled in moniterenter case. We actually acquired
2292       // the monitor after freezing all frames so nothing to do.
2293       preempt_kind = Continuation::freeze_on_monitorenter;
2294     }
2295     // Call this first to avoid racing with GC threads later when modifying the chunk flags.
2296     relativize_chunk_concurrently(chunk);
2297     chunk->set_preempted(false);
2298     retry_fast_path = true;
2299   } else {
2300     relativize_chunk_concurrently(chunk);
2301   }
2302 
2303   // On first thaw after freeze restore oops to the lockstack if any.
2304   assert(chunk->lockstack_size() == 0 || kind == Continuation::thaw_top, "");
2305   if (kind == Continuation::thaw_top && chunk->lockstack_size() > 0) {
2306     thaw_lockstack(chunk);
2307     retry_fast_path = true;
2308   }
2309 
2310   // Retry the fast path now that we possibly cleared the FLAG_HAS_LOCKSTACK
2311   // and FLAG_PREEMPTED flags from the stackChunk.
2312   if (retry_fast_path && can_thaw_fast(chunk)) {
2313     intptr_t* sp = thaw_fast<true>(chunk);
2314     if (_preempted_case) {
2315       return handle_preempted_continuation(sp, preempt_kind, true /* fast_case */);
2316     }
2317     return sp;
2318   }
2319 
2320   LogTarget(Trace, continuations) lt;
2321   if (lt.develop_is_enabled()) {
2322     LogStream ls(lt);
2323     ls.print_cr("thaw slow return_barrier: %d " INTPTR_FORMAT, kind, p2i(chunk));
2324     chunk->print_on(true, &ls);
2325   }
2326 
2327 #if CONT_JFR
2328   EventContinuationThawSlow e;
2329   if (e.should_commit()) {
2330     e.set_id(cast_from_oop<u8>(_cont.continuation()));
2331     e.commit();
2332   }
2333 #endif
2334 
2335   DEBUG_ONLY(_frames = 0;)
2336   _align_size = 0;
2337   int num_frames = kind == Continuation::thaw_top ? 2 : 1;
2338 
2339   _stream = StackChunkFrameStream<ChunkFrames::Mixed>(chunk);
2340   _top_unextended_sp_before_thaw = _stream.unextended_sp();
2341 
2342   frame heap_frame = _stream.to_frame();
2343   if (lt.develop_is_enabled()) {
2344     LogStream ls(lt);
2345     ls.print_cr("top hframe before (thaw):");
2346     assert(heap_frame.is_heap_frame(), "should have created a relative frame");
2347     heap_frame.print_value_on(&ls);
2348   }
2349 
2350   frame caller; // the thawed caller on the stack
2351   recurse_thaw(heap_frame, caller, num_frames, _preempted_case);
2352   finish_thaw(caller); // caller is now the topmost thawed frame
2353   _cont.write();
2354 
2355   assert(_cont.chunk_invariant(), "");
2356 
2357   JVMTI_ONLY(invalidate_jvmti_stack(_thread));
2358 
2359   _thread->set_cont_fastpath(_fastpath);
2360 
2361   intptr_t* sp = caller.sp();
2362 
2363   if (_preempted_case) {
2364     return handle_preempted_continuation(sp, preempt_kind, false /* fast_case */);
2365   }
2366   return sp;
2367 }
2368 
2369 void ThawBase::recurse_thaw(const frame& heap_frame, frame& caller, int num_frames, bool top_on_preempt_case) {
2370   log_develop_debug(continuations)("thaw num_frames: %d", num_frames);
2371   assert(!_cont.is_empty(), "no more frames");
2372   assert(num_frames > 0, "");
2373   assert(!heap_frame.is_empty(), "");
2374 
2375   if (top_on_preempt_case && (heap_frame.is_native_frame() || heap_frame.is_runtime_frame())) {
2376     heap_frame.is_native_frame() ? recurse_thaw_native_frame(heap_frame, caller, 2) : recurse_thaw_stub_frame(heap_frame, caller, 2);
2377   } else if (!heap_frame.is_interpreted_frame()) {
2378     recurse_thaw_compiled_frame(heap_frame, caller, num_frames, false);
2379   } else {
2380     recurse_thaw_interpreted_frame(heap_frame, caller, num_frames);
2381   }
2382 }
2383 
2384 template<typename FKind>
2385 bool ThawBase::recurse_thaw_java_frame(frame& caller, int num_frames) {
2386   assert(num_frames > 0, "");
2387 
2388   DEBUG_ONLY(_frames++;)
2389 
2390   int argsize = _stream.stack_argsize();
2391   CodeBlob* cb = _stream.cb();
2392 
2393   _stream.next(SmallRegisterMap::instance());
2394   assert(_stream.to_frame().is_empty() == _stream.is_done(), "");
2395 
2396   // We never leave a compiled caller of an interpreted frame as the top frame in the chunk
2397   // as it makes detecting that situation and adjusting unextended_sp tricky. We also always
2398   // thaw the caller of a frame that needs_stack_repair, as it would otherwise complicate things:
2399   // - Regardless of whether the frame was extended or not, we would need to copy the right arg
2400   //   size if its greater than the one given by the normal method signature (non-scalarized).
2401   // - If the frame was indeed extended, leaving its caller as the top frame would complicate walking
2402   //   the chunk (we need unextended_sp, but we only have sp).
2403   if (num_frames == 1 && !_stream.is_done() && ((FKind::interpreted && _stream.is_compiled()) || (FKind::compiled && cb->as_nmethod_or_null()->needs_stack_repair()))) {
2404     log_develop_trace(continuations)("thawing extra compiled frame to not leave a compiled interpreted-caller at top");
2405     num_frames++;
2406   }
2407 
2408   if (num_frames == 1 || _stream.is_done()) { // end recursion
2409     finalize_thaw(caller, FKind::interpreted ? 0 : argsize);
2410     return true; // bottom
2411   } else { // recurse
2412     recurse_thaw(_stream.to_frame(), caller, num_frames - 1, false /* top_on_preempt_case */);
2413     return false;
2414   }
2415 }
2416 
2417 void ThawBase::finalize_thaw(frame& entry, int argsize) {
2418   stackChunkOop chunk = _cont.tail();
2419 
2420   if (!_stream.is_done()) {
2421     assert(_stream.sp() >= chunk->sp_address(), "");
2422     chunk->set_sp(chunk->to_offset(_stream.sp()));
2423     chunk->set_pc(_stream.pc());
2424   } else {
2425     chunk->set_sp(chunk->bottom());
2426     chunk->set_pc(nullptr);
2427   }
2428   assert(_stream.is_done() == chunk->is_empty(), "");
2429 
2430   int total_thawed = pointer_delta_as_int(_stream.unextended_sp(), _top_unextended_sp_before_thaw);
2431   chunk->set_max_thawing_size(chunk->max_thawing_size() - total_thawed);
2432 
2433   _cont.set_argsize(argsize);
2434   entry = new_entry_frame();
2435 
2436   assert(entry.sp() == _cont.entrySP(), "");
2437   assert(Continuation::is_continuation_enterSpecial(entry), "");
2438   assert(_cont.is_entry_frame(entry), "");
2439 }
2440 
2441 inline void ThawBase::before_thaw_java_frame(const frame& hf, const frame& caller, bool bottom, int num_frame) {
2442   LogTarget(Trace, continuations) lt;
2443   if (lt.develop_is_enabled()) {
2444     LogStream ls(lt);
2445     ls.print_cr("======== THAWING FRAME: %d", num_frame);
2446     assert(hf.is_heap_frame(), "should be");
2447     hf.print_value_on(&ls);
2448   }
2449   assert(bottom == _cont.is_entry_frame(caller), "bottom: %d is_entry_frame: %d", bottom, _cont.is_entry_frame(hf));
2450 }
2451 
2452 inline void ThawBase::after_thaw_java_frame(const frame& f, bool bottom) {
2453 #ifdef ASSERT
2454   LogTarget(Trace, continuations) lt;
2455   if (lt.develop_is_enabled()) {
2456     LogStream ls(lt);
2457     ls.print_cr("thawed frame:");
2458     print_frame_layout(f, false, &ls); // f.print_on(&ls);
2459   }
2460 #endif
2461 }
2462 
2463 inline void ThawBase::patch(frame& f, const frame& caller, bool bottom, bool augmented) {
2464   assert(!bottom || caller.fp() == _cont.entryFP(), "");
2465   if (bottom) {
2466     ContinuationHelper::Frame::patch_pc(caller, _cont.is_empty() ? caller.pc()
2467                                                                  : StubRoutines::cont_returnBarrier());
2468   } else if (caller.is_compiled_frame()){
2469     // caller might have been deoptimized during thaw but we've overwritten the return address when copying f from the heap.
2470     // If the caller is not deoptimized, pc is unchanged.
2471     ContinuationHelper::Frame::patch_pc(caller, caller.raw_pc(), augmented /*callee_augmented*/);
2472   }
2473 
2474   patch_pd(f, caller);
2475 
2476   if (f.is_interpreted_frame()) {
2477     ContinuationHelper::InterpretedFrame::patch_sender_sp(f, caller);
2478   }
2479 
2480   assert(!bottom || !_cont.is_empty() || Continuation::is_continuation_entry_frame(f, nullptr), "");
2481   assert(!bottom || (_cont.is_empty() != Continuation::is_cont_barrier_frame(f)), "");
2482 }
2483 
2484 void ThawBase::clear_bitmap_bits(address start, address end) {
2485   assert(is_aligned(start, wordSize), "should be aligned: " PTR_FORMAT, p2i(start));
2486   assert(is_aligned(end, VMRegImpl::stack_slot_size), "should be aligned: " PTR_FORMAT, p2i(end));
2487 
2488   // we need to clear the bits that correspond to arguments as they reside in the caller frame
2489   // or they will keep objects that are otherwise unreachable alive.
2490 
2491   // Align `end` if UseCompressedOops is not set to avoid UB when calculating the bit index, since
2492   // `end` could be at an odd number of stack slots from `start`, i.e might not be oop aligned.
2493   // If that's the case the bit range corresponding to the last stack slot should not have bits set
2494   // anyways and we assert that before returning.
2495   address effective_end = UseCompressedOops ? end : align_down(end, wordSize);
2496   log_develop_trace(continuations)("clearing bitmap for " INTPTR_FORMAT " - " INTPTR_FORMAT, p2i(start), p2i(effective_end));
2497   stackChunkOop chunk = _cont.tail();
2498   chunk->bitmap().clear_range(chunk->bit_index_for(start), chunk->bit_index_for(effective_end));
2499   assert(effective_end == end || !chunk->bitmap().at(chunk->bit_index_for(effective_end)), "bit should not be set");
2500 }
2501 
2502 intptr_t* ThawBase::handle_preempted_continuation(intptr_t* sp, Continuation::preempt_kind preempt_kind, bool fast_case) {
2503   assert(preempt_kind == Continuation::freeze_on_wait || preempt_kind == Continuation::freeze_on_monitorenter, "");
2504   frame top(sp);
2505   assert(top.pc() == *(address*)(sp - frame::sender_sp_ret_address_offset()), "");
2506 
2507 #if INCLUDE_JVMTI
2508   // Finish the VTMS transition.
2509   assert(_thread->is_in_VTMS_transition(), "must be");
2510   bool is_vthread = Continuation::continuation_scope(_cont.continuation()) == java_lang_VirtualThread::vthread_scope();
2511   if (is_vthread) {
2512     if (JvmtiVTMSTransitionDisabler::VTMS_notify_jvmti_events()) {
2513       jvmti_mount_end(_thread, _cont, top);
2514     } else {
2515       _thread->set_is_in_VTMS_transition(false);
2516       java_lang_Thread::set_is_in_VTMS_transition(_thread->vthread(), false);
2517     }
2518   }
2519 #endif
2520 
2521   if (fast_case) {
2522     // If we thawed in the slow path the runtime stub/native wrapper frame already
2523     // has the correct fp (see ThawBase::new_stack_frame). On the fast path though,
2524     // we copied the fp patched during freeze, which will now have to be fixed.
2525     assert(top.is_runtime_frame() || top.is_native_frame(), "");
2526     int fsize = top.cb()->frame_size();
2527     patch_pd(top, sp + fsize);
2528   }
2529 
2530   if (preempt_kind == Continuation::freeze_on_wait) {
2531     // Check now if we need to throw IE exception.
2532     if (_thread->pending_interrupted_exception()) {
2533       throw_interrupted_exception(_thread, top);
2534       _thread->set_pending_interrupted_exception(false);
2535     }
2536   } else if (top.is_runtime_frame()) {
2537     // The continuation might now run on a different platform thread than the previous time so
2538     // we need to adjust the current thread saved in the stub frame before restoring registers.
2539     JavaThread** thread_addr = frame::saved_thread_address(top);
2540     if (thread_addr != nullptr) *thread_addr = _thread;
2541   }
2542   return sp;
2543 }
2544 
2545 void ThawBase::throw_interrupted_exception(JavaThread* current, frame& top) {
2546   ContinuationWrapper::SafepointOp so(current, _cont);
2547   // Since we might safepoint set the anchor so that the stack can be walked.
2548   set_anchor(current, top.sp());
2549   JRT_BLOCK
2550     THROW(vmSymbols::java_lang_InterruptedException());
2551   JRT_BLOCK_END
2552   clear_anchor(current);
2553 }
2554 
2555 NOINLINE void ThawBase::recurse_thaw_interpreted_frame(const frame& hf, frame& caller, int num_frames) {
2556   assert(hf.is_interpreted_frame(), "");
2557 
2558   if (UNLIKELY(seen_by_gc())) {
2559     _cont.tail()->do_barriers<stackChunkOopDesc::BarrierType::Store>(_stream, SmallRegisterMap::instance());
2560   }
2561 
2562   const bool is_bottom_frame = recurse_thaw_java_frame<ContinuationHelper::InterpretedFrame>(caller, num_frames);
2563 
2564   DEBUG_ONLY(before_thaw_java_frame(hf, caller, is_bottom_frame, num_frames);)
2565 
2566   _align_size += frame::align_wiggle; // possible added alignment for internal interpreted frame alignment om AArch64
2567 
2568   frame f = new_stack_frame<ContinuationHelper::InterpretedFrame>(hf, caller, is_bottom_frame);
2569 
2570   intptr_t* const stack_frame_top = f.sp() + frame::metadata_words_at_top;
2571   intptr_t* const stack_frame_bottom = ContinuationHelper::InterpretedFrame::frame_bottom(f);
2572   intptr_t* const heap_frame_top = hf.unextended_sp() + frame::metadata_words_at_top;
2573   intptr_t* const heap_frame_bottom = ContinuationHelper::InterpretedFrame::frame_bottom(hf);
2574 
2575   assert(hf.is_heap_frame(), "should be");
2576   assert(!f.is_heap_frame(), "should not be");
2577 
2578   const int fsize = pointer_delta_as_int(heap_frame_bottom, heap_frame_top);
2579   assert((stack_frame_bottom == stack_frame_top + fsize), "");
2580 
2581   // Some architectures (like AArch64/PPC64/RISC-V) add padding between the locals and the fixed_frame to keep the fp 16-byte-aligned.
2582   // On those architectures we freeze the padding in order to keep the same fp-relative offsets in the fixed_frame.
2583   copy_from_chunk(heap_frame_top, stack_frame_top, fsize);
2584 
2585   // Make sure the relativized locals is already set.
2586   assert(f.interpreter_frame_local_at(0) == stack_frame_bottom - 1, "invalid frame bottom");
2587 
2588   derelativize_interpreted_frame_metadata(hf, f);
2589   patch(f, caller, is_bottom_frame);
2590 
2591   assert(f.is_interpreted_frame_valid(_cont.thread()), "invalid thawed frame");
2592   assert(stack_frame_bottom <= ContinuationHelper::Frame::frame_top(caller), "");
2593 
2594   CONT_JFR_ONLY(_jfr_info.record_interpreted_frame();)
2595 
2596   maybe_set_fastpath(f.sp());
2597 
2598   Method* m = hf.interpreter_frame_method();
2599   assert(!m->is_native() || !is_bottom_frame, "should be top frame of thaw_top case; missing caller frame");
2600   const int locals = m->max_locals();
2601 
2602   if (!is_bottom_frame) {
2603     // can only fix caller once this frame is thawed (due to callee saved regs)
2604     _cont.tail()->fix_thawed_frame(caller, SmallRegisterMap::instance());
2605   } else if (_cont.tail()->has_bitmap() && locals > 0) {
2606     assert(hf.is_heap_frame(), "should be");
2607     address start = (address)(heap_frame_bottom - locals);
2608     address end = (address)heap_frame_bottom;
2609     clear_bitmap_bits(start, end);
2610   }
2611 
2612   DEBUG_ONLY(after_thaw_java_frame(f, is_bottom_frame);)
2613   caller = f;
2614 }
2615 
2616 void ThawBase::recurse_thaw_compiled_frame(const frame& hf, frame& caller, int num_frames, bool stub_caller) {
2617   assert(hf.is_compiled_frame(), "");
2618   assert(_preempted_case || !stub_caller, "stub caller not at preemption");
2619 
2620   if (!stub_caller && UNLIKELY(seen_by_gc())) { // recurse_thaw_stub_frame already invoked our barriers with a full regmap
2621     _cont.tail()->do_barriers<stackChunkOopDesc::BarrierType::Store>(_stream, SmallRegisterMap::instance());
2622   }
2623 
2624   const bool is_bottom_frame = recurse_thaw_java_frame<ContinuationHelper::CompiledFrame>(caller, num_frames);
2625 
2626   DEBUG_ONLY(before_thaw_java_frame(hf, caller, is_bottom_frame, num_frames);)
2627 
2628   assert(caller.sp() == caller.unextended_sp(), "");
2629 
2630   if ((!is_bottom_frame && caller.is_interpreted_frame()) || (is_bottom_frame && Interpreter::contains(_cont.tail()->pc()))) {
2631     _align_size += frame::align_wiggle; // we add one whether or not we've aligned because we add it in recurse_freeze_compiled_frame
2632   }
2633 
2634   int fsize = 0;
2635   int added_argsize = 0;
2636   bool augmented = hf.was_augmented_on_entry(fsize);
2637   if (!augmented) {
2638     added_argsize = (is_bottom_frame || caller.is_interpreted_frame()) ? hf.compiled_frame_stack_argsize() : 0;
2639     fsize += added_argsize;
2640   }
2641   assert(!is_bottom_frame || !augmented, "");
2642 
2643 
2644   // new_stack_frame must construct the resulting frame using hf.pc() rather than hf.raw_pc() because the frame is not
2645   // yet laid out in the stack, and so the original_pc is not stored in it.
2646   // As a result, f.is_deoptimized_frame() is always false and we must test hf to know if the frame is deoptimized.
2647   frame f = new_stack_frame<ContinuationHelper::CompiledFrame>(hf, caller, is_bottom_frame, augmented ? fsize - hf.cb()->frame_size() : 0);
2648   assert(f.cb()->frame_size() == (int)(caller.sp() - f.sp()), "");
2649 
2650   intptr_t* const stack_frame_top = f.sp();
2651   intptr_t* const heap_frame_top = hf.unextended_sp();
2652   intptr_t* from = heap_frame_top - frame::metadata_words_at_bottom;
2653   intptr_t* to   = stack_frame_top - frame::metadata_words_at_bottom;
2654   // copy metadata, except the metadata at the top of the (unextended) entry frame
2655   int sz = fsize + frame::metadata_words_at_bottom + (is_bottom_frame && added_argsize == 0 ? 0 : frame::metadata_words_at_top);
2656 
2657   // If we're the bottom-most thawed frame, we're writing to within one word from entrySP
2658   // (we might have one padding word for alignment)
2659   assert(!is_bottom_frame || (_cont.entrySP() - 1 <= to + sz && to + sz <= _cont.entrySP()), "");
2660   assert(!is_bottom_frame || hf.compiled_frame_stack_argsize() != 0 || (to + sz && to + sz == _cont.entrySP()), "");
2661 
2662   copy_from_chunk(from, to, sz); // copying good oops because we invoked barriers above
2663 
2664   patch(f, caller, is_bottom_frame, augmented);
2665 
2666   // f.is_deoptimized_frame() is always false and we must test hf.is_deoptimized_frame() (see comment above)
2667   assert(!f.is_deoptimized_frame(), "");
2668   if (hf.is_deoptimized_frame()) {
2669     maybe_set_fastpath(f.sp());
2670   } else if (_thread->is_interp_only_mode()
2671               || (stub_caller && f.cb()->as_nmethod()->is_marked_for_deoptimization())) {
2672     // The caller of the safepoint stub when the continuation is preempted is not at a call instruction, and so
2673     // cannot rely on nmethod patching for deopt.
2674     assert(_thread->is_interp_only_mode() || stub_caller, "expected a stub-caller");
2675 
2676     log_develop_trace(continuations)("Deoptimizing thawed frame");
2677     DEBUG_ONLY(ContinuationHelper::Frame::patch_pc(f, nullptr));
2678 
2679     f.deoptimize(nullptr); // the null thread simply avoids the assertion in deoptimize which we're not set up for
2680     assert(f.is_deoptimized_frame(), "");
2681     assert(ContinuationHelper::Frame::is_deopt_return(f.raw_pc(), f), "");
2682     maybe_set_fastpath(f.sp());
2683   }
2684 
2685   if (!is_bottom_frame) {
2686     // can only fix caller once this frame is thawed (due to callee saved regs); this happens on the stack
2687     _cont.tail()->fix_thawed_frame(caller, SmallRegisterMap::instance());
2688   } else if (_cont.tail()->has_bitmap() && added_argsize > 0) {
2689     address start = (address)(heap_frame_top + ContinuationHelper::CompiledFrame::size(hf) + frame::metadata_words_at_top);
2690     int stack_args_slots = f.cb()->as_nmethod()->num_stack_arg_slots(false /* rounded */);
2691     int argsize_in_bytes = stack_args_slots * VMRegImpl::stack_slot_size;
2692     clear_bitmap_bits(start, start + argsize_in_bytes);
2693   }
2694 
2695   DEBUG_ONLY(after_thaw_java_frame(f, is_bottom_frame);)
2696   caller = f;
2697 }
2698 
2699 void ThawBase::recurse_thaw_stub_frame(const frame& hf, frame& caller, int num_frames) {
2700   DEBUG_ONLY(_frames++;)
2701 
2702   if (UNLIKELY(seen_by_gc())) {
2703     // Process the stub's caller here since we might need the full map.
2704     RegisterMap map(nullptr,
2705                     RegisterMap::UpdateMap::include,
2706                     RegisterMap::ProcessFrames::skip,
2707                     RegisterMap::WalkContinuation::skip);
2708     map.set_include_argument_oops(false);
2709     _stream.next(&map);
2710     assert(!_stream.is_done(), "");
2711     _cont.tail()->do_barriers<stackChunkOopDesc::BarrierType::Store>(_stream, &map);
2712   } else {
2713     _stream.next(SmallRegisterMap::instance());
2714     assert(!_stream.is_done(), "");
2715   }
2716 
2717   recurse_thaw_compiled_frame(_stream.to_frame(), caller, num_frames, true);
2718 
2719   assert(caller.is_compiled_frame(), "");
2720   assert(caller.sp() == caller.unextended_sp(), "");
2721 
2722   DEBUG_ONLY(before_thaw_java_frame(hf, caller, false /*is_bottom_frame*/, num_frames);)
2723 
2724   frame f = new_stack_frame<ContinuationHelper::StubFrame>(hf, caller, false);
2725   intptr_t* stack_frame_top = f.sp();
2726   intptr_t* heap_frame_top = hf.sp();
2727   int fsize = ContinuationHelper::StubFrame::size(hf);
2728 
2729   copy_from_chunk(heap_frame_top - frame::metadata_words, stack_frame_top - frame::metadata_words,
2730                   fsize + frame::metadata_words);
2731 
2732   patch(f, caller, false /*is_bottom_frame*/);
2733 
2734   // can only fix caller once this frame is thawed (due to callee saved regs)
2735   RegisterMap map(nullptr,
2736                   RegisterMap::UpdateMap::include,
2737                   RegisterMap::ProcessFrames::skip,
2738                   RegisterMap::WalkContinuation::skip);
2739   map.set_include_argument_oops(false);
2740   f.oop_map()->update_register_map(&f, &map);
2741   ContinuationHelper::update_register_map_with_callee(caller, &map);
2742   _cont.tail()->fix_thawed_frame(caller, &map);
2743 
2744   DEBUG_ONLY(after_thaw_java_frame(f, false /*is_bottom_frame*/);)
2745   caller = f;
2746 }
2747 
2748 void ThawBase::recurse_thaw_native_frame(const frame& hf, frame& caller, int num_frames) {
2749   assert(hf.is_native_frame(), "");
2750   assert(_preempted_case && hf.cb()->as_nmethod()->method()->is_object_wait0(), "");
2751 
2752   if (UNLIKELY(seen_by_gc())) { // recurse_thaw_stub_frame already invoked our barriers with a full regmap
2753     _cont.tail()->do_barriers<stackChunkOopDesc::BarrierType::Store>(_stream, SmallRegisterMap::instance());
2754   }
2755 
2756   const bool is_bottom_frame = recurse_thaw_java_frame<ContinuationHelper::NativeFrame>(caller, num_frames);
2757   assert(!is_bottom_frame, "");
2758 
2759   DEBUG_ONLY(before_thaw_java_frame(hf, caller, is_bottom_frame, num_frames);)
2760 
2761   assert(caller.sp() == caller.unextended_sp(), "");
2762 
2763   if (caller.is_interpreted_frame()) {
2764     _align_size += frame::align_wiggle; // we add one whether or not we've aligned because we add it in recurse_freeze_native_frame
2765   }
2766 
2767   // new_stack_frame must construct the resulting frame using hf.pc() rather than hf.raw_pc() because the frame is not
2768   // yet laid out in the stack, and so the original_pc is not stored in it.
2769   // As a result, f.is_deoptimized_frame() is always false and we must test hf to know if the frame is deoptimized.
2770   frame f = new_stack_frame<ContinuationHelper::NativeFrame>(hf, caller, false /* bottom */);
2771   intptr_t* const stack_frame_top = f.sp();
2772   intptr_t* const heap_frame_top = hf.unextended_sp();
2773 
2774   int fsize = ContinuationHelper::NativeFrame::size(hf);
2775   assert(fsize <= (int)(caller.unextended_sp() - f.unextended_sp()), "");
2776 
2777   intptr_t* from = heap_frame_top - frame::metadata_words_at_bottom;
2778   intptr_t* to   = stack_frame_top - frame::metadata_words_at_bottom;
2779   int sz = fsize + frame::metadata_words_at_bottom;
2780 
2781   copy_from_chunk(from, to, sz); // copying good oops because we invoked barriers above
2782 
2783   patch(f, caller, false /* bottom */);
2784 
2785   // f.is_deoptimized_frame() is always false and we must test hf.is_deoptimized_frame() (see comment above)
2786   assert(!f.is_deoptimized_frame(), "");
2787   assert(!hf.is_deoptimized_frame(), "");
2788   assert(!f.cb()->as_nmethod()->is_marked_for_deoptimization(), "");
2789 
2790   // can only fix caller once this frame is thawed (due to callee saved regs); this happens on the stack
2791   _cont.tail()->fix_thawed_frame(caller, SmallRegisterMap::instance());
2792 
2793   DEBUG_ONLY(after_thaw_java_frame(f, false /* bottom */);)
2794   caller = f;
2795 }
2796 
2797 void ThawBase::finish_thaw(frame& f) {
2798   stackChunkOop chunk = _cont.tail();
2799 
2800   if (chunk->is_empty()) {
2801     // Only remove chunk from list if it can't be reused for another freeze
2802     if (seen_by_gc()) {
2803       _cont.set_tail(chunk->parent());
2804     } else {
2805       chunk->set_has_mixed_frames(false);
2806     }
2807     chunk->set_max_thawing_size(0);
2808   } else {
2809     chunk->set_max_thawing_size(chunk->max_thawing_size() - _align_size);
2810   }
2811   assert(chunk->is_empty() == (chunk->max_thawing_size() == 0), "");
2812 
2813   if (!is_aligned(f.sp(), frame::frame_alignment)) {
2814     assert(f.is_interpreted_frame(), "");
2815     f.set_sp(align_down(f.sp(), frame::frame_alignment));
2816   }
2817   push_return_frame(f);
2818   chunk->fix_thawed_frame(f, SmallRegisterMap::instance()); // can only fix caller after push_return_frame (due to callee saved regs)
2819 
2820   assert(_cont.is_empty() == _cont.last_frame().is_empty(), "");
2821 
2822   log_develop_trace(continuations)("thawed %d frames", _frames);
2823 
2824   LogTarget(Trace, continuations) lt;
2825   if (lt.develop_is_enabled()) {
2826     LogStream ls(lt);
2827     ls.print_cr("top hframe after (thaw):");
2828     _cont.last_frame().print_value_on(&ls);
2829   }
2830 }
2831 
2832 void ThawBase::push_return_frame(frame& f) { // see generate_cont_thaw
2833   assert(!f.is_compiled_frame() || f.is_deoptimized_frame() == f.cb()->as_nmethod()->is_deopt_pc(f.raw_pc()), "");
2834   assert(!f.is_compiled_frame() || f.is_deoptimized_frame() == (f.pc() != f.raw_pc()), "");
2835 
2836   LogTarget(Trace, continuations) lt;
2837   if (lt.develop_is_enabled()) {
2838     LogStream ls(lt);
2839     ls.print_cr("push_return_frame");
2840     f.print_value_on(&ls);
2841   }
2842 
2843   assert(f.sp() - frame::metadata_words_at_bottom >= _top_stack_address, "overwrote past thawing space"
2844     " to: " INTPTR_FORMAT " top_address: " INTPTR_FORMAT, p2i(f.sp() - frame::metadata_words), p2i(_top_stack_address));
2845   ContinuationHelper::Frame::patch_pc(f, f.raw_pc()); // in case we want to deopt the frame in a full transition, this is checked.
2846   ContinuationHelper::push_pd(f);
2847 
2848   assert(ContinuationHelper::Frame::assert_frame_laid_out(f), "");
2849 }
2850 
2851 // returns new top sp
2852 // called after preparations (stack overflow check and making room)
2853 template<typename ConfigT>
2854 static inline intptr_t* thaw_internal(JavaThread* thread, const Continuation::thaw_kind kind) {
2855   assert(thread == JavaThread::current(), "Must be current thread");
2856 
2857   CONT_JFR_ONLY(EventContinuationThaw event;)
2858 
2859   log_develop_trace(continuations)("~~~~ thaw kind: %d sp: " INTPTR_FORMAT, kind, p2i(thread->last_continuation()->entry_sp()));
2860 
2861   ContinuationEntry* entry = thread->last_continuation();
2862   assert(entry != nullptr, "");
2863   oop oopCont = entry->cont_oop(thread);
2864 
2865   assert(!jdk_internal_vm_Continuation::done(oopCont), "");
2866   assert(oopCont == get_continuation(thread), "");
2867   verify_continuation(oopCont);
2868 
2869   assert(entry->is_virtual_thread() == (entry->scope(thread) == java_lang_VirtualThread::vthread_scope()), "");
2870 
2871   ContinuationWrapper cont(thread, oopCont);
2872   log_develop_debug(continuations)("THAW #" INTPTR_FORMAT " " INTPTR_FORMAT, cont.hash(), p2i((oopDesc*)oopCont));
2873 
2874 #ifdef ASSERT
2875   set_anchor_to_entry(thread, cont.entry());
2876   log_frames(thread);
2877   clear_anchor(thread);
2878 #endif
2879 
2880   DEBUG_ONLY(bool preempted = cont.tail()->preempted();)
2881   Thaw<ConfigT> thw(thread, cont);
2882   intptr_t* const sp = thw.thaw(kind);
2883   assert(is_aligned(sp, frame::frame_alignment), "");
2884   DEBUG_ONLY(log_frames_after_thaw(thread, cont, sp, preempted);)
2885 
2886   CONT_JFR_ONLY(thw.jfr_info().post_jfr_event(&event, cont.continuation(), thread);)
2887 
2888   verify_continuation(cont.continuation());
2889   log_develop_debug(continuations)("=== End of thaw #" INTPTR_FORMAT, cont.hash());
2890 
2891   return sp;
2892 }
2893 
2894 #ifdef ASSERT
2895 static void do_deopt_after_thaw(JavaThread* thread) {
2896   int i = 0;
2897   StackFrameStream fst(thread, true, false);
2898   fst.register_map()->set_include_argument_oops(false);
2899   ContinuationHelper::update_register_map_with_callee(*fst.current(), fst.register_map());
2900   for (; !fst.is_done(); fst.next()) {
2901     if (fst.current()->cb()->is_nmethod()) {
2902       nmethod* nm = fst.current()->cb()->as_nmethod();
2903       if (!nm->method()->is_continuation_native_intrinsic()) {
2904         nm->make_deoptimized();
2905       }
2906     }
2907   }
2908 }
2909 
2910 class ThawVerifyOopsClosure: public OopClosure {
2911   intptr_t* _p;
2912   outputStream* _st;
2913   bool is_good_oop(oop o) {
2914     return dbg_is_safe(o, -1) && dbg_is_safe(o->klass(), -1) && oopDesc::is_oop(o) && o->klass()->is_klass();
2915   }
2916 public:
2917   ThawVerifyOopsClosure(outputStream* st) : _p(nullptr), _st(st) {}
2918   intptr_t* p() { return _p; }
2919   void reset() { _p = nullptr; }
2920 
2921   virtual void do_oop(oop* p) {
2922     oop o = *p;
2923     if (o == nullptr || is_good_oop(o)) {
2924       return;
2925     }
2926     _p = (intptr_t*)p;
2927     _st->print_cr("*** non-oop " PTR_FORMAT " found at " PTR_FORMAT, p2i(*p), p2i(p));
2928   }
2929   virtual void do_oop(narrowOop* p) {
2930     oop o = RawAccess<>::oop_load(p);
2931     if (o == nullptr || is_good_oop(o)) {
2932       return;
2933     }
2934     _p = (intptr_t*)p;
2935     _st->print_cr("*** (narrow) non-oop %x found at " PTR_FORMAT, (int)(*p), p2i(p));
2936   }
2937 };
2938 
2939 static bool do_verify_after_thaw(JavaThread* thread, stackChunkOop chunk, outputStream* st) {
2940   assert(thread->has_last_Java_frame(), "");
2941 
2942   ResourceMark rm;
2943   ThawVerifyOopsClosure cl(st);
2944   NMethodToOopClosure cf(&cl, false);
2945 
2946   StackFrameStream fst(thread, true, false);
2947   fst.register_map()->set_include_argument_oops(false);
2948   ContinuationHelper::update_register_map_with_callee(*fst.current(), fst.register_map());
2949   for (; !fst.is_done() && !Continuation::is_continuation_enterSpecial(*fst.current()); fst.next()) {
2950     if (fst.current()->cb()->is_nmethod() && fst.current()->cb()->as_nmethod()->is_marked_for_deoptimization()) {
2951       st->print_cr(">>> do_verify_after_thaw deopt");
2952       fst.current()->deoptimize(nullptr);
2953       fst.current()->print_on(st);
2954     }
2955 
2956     fst.current()->oops_do(&cl, &cf, fst.register_map());
2957     if (cl.p() != nullptr) {
2958       frame fr = *fst.current();
2959       st->print_cr("Failed for frame barriers: %d",chunk->requires_barriers());
2960       fr.print_on(st);
2961       if (!fr.is_interpreted_frame()) {
2962         st->print_cr("size: %d argsize: %d",
2963                      ContinuationHelper::NonInterpretedUnknownFrame::size(fr),
2964                      ContinuationHelper::NonInterpretedUnknownFrame::stack_argsize(fr));
2965       }
2966       VMReg reg = fst.register_map()->find_register_spilled_here(cl.p(), fst.current()->sp());
2967       if (reg != nullptr) {
2968         st->print_cr("Reg %s %d", reg->name(), reg->is_stack() ? (int)reg->reg2stack() : -99);
2969       }
2970       cl.reset();
2971       DEBUG_ONLY(thread->print_frame_layout();)
2972       if (chunk != nullptr) {
2973         chunk->print_on(true, st);
2974       }
2975       return false;
2976     }
2977   }
2978   return true;
2979 }
2980 
2981 static void log_frames(JavaThread* thread) {
2982   const static int show_entry_callers = 3;
2983   LogTarget(Trace, continuations) lt;
2984   if (!lt.develop_is_enabled()) {
2985     return;
2986   }
2987   LogStream ls(lt);
2988 
2989   ls.print_cr("------- frames --------- for thread " INTPTR_FORMAT, p2i(thread));
2990   if (!thread->has_last_Java_frame()) {
2991     ls.print_cr("NO ANCHOR!");
2992   }
2993 
2994   RegisterMap map(thread,
2995                   RegisterMap::UpdateMap::include,
2996                   RegisterMap::ProcessFrames::include,
2997                   RegisterMap::WalkContinuation::skip);
2998   map.set_include_argument_oops(false);
2999 
3000   if (false) {
3001     for (frame f = thread->last_frame(); !f.is_entry_frame(); f = f.sender(&map)) {
3002       f.print_on(&ls);
3003     }
3004   } else {
3005     map.set_skip_missing(true);
3006     ResetNoHandleMark rnhm;
3007     ResourceMark rm;
3008     HandleMark hm(Thread::current());
3009     FrameValues values;
3010 
3011     int i = 0;
3012     int post_entry = -1;
3013     for (frame f = thread->last_frame(); !f.is_first_frame(); f = f.sender(&map), i++) {
3014       f.describe(values, i, &map, i == 0);
3015       if (post_entry >= 0 || Continuation::is_continuation_enterSpecial(f))
3016         post_entry++;
3017       if (post_entry >= show_entry_callers)
3018         break;
3019     }
3020     values.print_on(thread, &ls);
3021   }
3022 
3023   ls.print_cr("======= end frames =========");
3024 }
3025 
3026 static void log_frames_after_thaw(JavaThread* thread, ContinuationWrapper& cont, intptr_t* sp, bool preempted) {
3027   intptr_t* sp0 = sp;
3028   address pc0 = *(address*)(sp - frame::sender_sp_ret_address_offset());
3029 
3030   if (preempted && sp0 == cont.entrySP()) {
3031     // Still preempted (monitor not acquired) so no frames were thawed.
3032     assert(cont.tail()->preempted(), "");
3033     set_anchor(thread, cont.entrySP(), cont.entryPC());
3034   } else {
3035     set_anchor(thread, sp0);
3036   }
3037 
3038   log_frames(thread);
3039   if (LoomVerifyAfterThaw) {
3040     assert(do_verify_after_thaw(thread, cont.tail(), tty), "");
3041   }
3042   assert(ContinuationEntry::assert_entry_frame_laid_out(thread), "");
3043   clear_anchor(thread);
3044 
3045   LogTarget(Trace, continuations) lt;
3046   if (lt.develop_is_enabled()) {
3047     LogStream ls(lt);
3048     ls.print_cr("Jumping to frame (thaw):");
3049     frame(sp).print_value_on(&ls);
3050   }
3051 }
3052 #endif // ASSERT
3053 
3054 #include CPU_HEADER_INLINE(continuationFreezeThaw)
3055 
3056 #ifdef ASSERT
3057 static void print_frame_layout(const frame& f, bool callee_complete, outputStream* st) {
3058   ResourceMark rm;
3059   FrameValues values;
3060   assert(f.get_cb() != nullptr, "");
3061   RegisterMap map(f.is_heap_frame() ?
3062                     nullptr :
3063                     JavaThread::current(),
3064                   RegisterMap::UpdateMap::include,
3065                   RegisterMap::ProcessFrames::skip,
3066                   RegisterMap::WalkContinuation::skip);
3067   map.set_include_argument_oops(false);
3068   map.set_skip_missing(true);
3069   if (callee_complete) {
3070     frame::update_map_with_saved_link(&map, ContinuationHelper::Frame::callee_link_address(f));
3071   }
3072   const_cast<frame&>(f).describe(values, 0, &map, true);
3073   values.print_on(static_cast<JavaThread*>(nullptr), st);
3074 }
3075 #endif
3076 
3077 static address thaw_entry   = nullptr;
3078 static address freeze_entry = nullptr;
3079 static address freeze_preempt_entry = nullptr;
3080 
3081 address Continuation::thaw_entry() {
3082   return ::thaw_entry;
3083 }
3084 
3085 address Continuation::freeze_entry() {
3086   return ::freeze_entry;
3087 }
3088 
3089 address Continuation::freeze_preempt_entry() {
3090   return ::freeze_preempt_entry;
3091 }
3092 
3093 class ConfigResolve {
3094 public:
3095   static void resolve() { resolve_compressed(); }
3096 
3097   static void resolve_compressed() {
3098     UseCompressedOops ? resolve_gc<true>()
3099                       : resolve_gc<false>();
3100   }
3101 
3102 private:
3103   template <bool use_compressed>
3104   static void resolve_gc() {
3105     BarrierSet* bs = BarrierSet::barrier_set();
3106     assert(bs != nullptr, "freeze/thaw invoked before BarrierSet is set");
3107     switch (bs->kind()) {
3108 #define BARRIER_SET_RESOLVE_BARRIER_CLOSURE(bs_name)                    \
3109       case BarrierSet::bs_name: {                                       \
3110         resolve<use_compressed, typename BarrierSet::GetType<BarrierSet::bs_name>::type>(); \
3111       }                                                                 \
3112         break;
3113       FOR_EACH_CONCRETE_BARRIER_SET_DO(BARRIER_SET_RESOLVE_BARRIER_CLOSURE)
3114 #undef BARRIER_SET_RESOLVE_BARRIER_CLOSURE
3115 
3116     default:
3117       fatal("BarrierSet resolving not implemented");
3118     };
3119   }
3120 
3121   template <bool use_compressed, typename BarrierSetT>
3122   static void resolve() {
3123     typedef Config<use_compressed ? oop_kind::NARROW : oop_kind::WIDE, BarrierSetT> SelectedConfigT;
3124 
3125     freeze_entry = (address)freeze<SelectedConfigT>;
3126     freeze_preempt_entry = (address)SelectedConfigT::freeze_preempt;
3127 
3128     // If we wanted, we could templatize by kind and have three different thaw entries
3129     thaw_entry   = (address)thaw<SelectedConfigT>;
3130   }
3131 };
3132 
3133 void Continuation::init() {
3134   ConfigResolve::resolve();
3135 }