1 /*
   2  * Copyright (c) 2018, 2026, 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 "cppstdlib/type_traits.hpp"
  32 #include "gc/shared/barrierSet.hpp"
  33 #include "gc/shared/continuationGCSupport.inline.hpp"
  34 #include "gc/shared/gc_globals.hpp"
  35 #include "gc/shared/memAllocator.hpp"
  36 #include "gc/shared/threadLocalAllocBuffer.inline.hpp"
  37 #include "interpreter/bytecodeStream.hpp"
  38 #include "interpreter/interpreter.hpp"
  39 #include "interpreter/interpreterRuntime.hpp"
  40 #include "jfr/jfrEvents.hpp"
  41 #include "logging/log.hpp"
  42 #include "logging/logStream.hpp"
  43 #include "oops/access.inline.hpp"
  44 #include "oops/constantPool.inline.hpp"
  45 #include "oops/method.inline.hpp"
  46 #include "oops/objArrayOop.inline.hpp"
  47 #include "oops/oopsHierarchy.hpp"
  48 #include "oops/stackChunkOop.inline.hpp"
  49 #include "prims/jvmtiThreadState.hpp"
  50 #include "runtime/arguments.hpp"
  51 #include "runtime/continuation.hpp"
  52 #include "runtime/continuationEntry.inline.hpp"
  53 #include "runtime/continuationHelper.inline.hpp"
  54 #include "runtime/continuationJavaClasses.inline.hpp"
  55 #include "runtime/continuationWrapper.inline.hpp"
  56 #include "runtime/frame.inline.hpp"
  57 #include "runtime/interfaceSupport.inline.hpp"
  58 #include "runtime/javaThread.inline.hpp"
  59 #include "runtime/jniHandles.inline.hpp"
  60 #include "runtime/keepStackGCProcessed.hpp"
  61 #include "runtime/mountUnmountDisabler.hpp"
  62 #include "runtime/objectMonitor.inline.hpp"
  63 #include "runtime/orderAccess.hpp"
  64 #include "runtime/prefetch.inline.hpp"
  65 #include "runtime/sharedRuntime.hpp"
  66 #include "runtime/smallRegisterMap.inline.hpp"
  67 #include "runtime/stackChunkFrameStream.inline.hpp"
  68 #include "runtime/stackFrameStream.inline.hpp"
  69 #include "runtime/stackOverflow.hpp"
  70 #include "runtime/stackWatermarkSet.inline.hpp"
  71 #include "runtime/vframe.inline.hpp"
  72 #include "runtime/vframe_hp.hpp"
  73 #include "utilities/debug.hpp"
  74 #include "utilities/exceptions.hpp"
  75 #include "utilities/macros.hpp"
  76 #include "utilities/vmError.hpp"
  77 #if INCLUDE_SHENANDOAHGC
  78 #include "gc/shenandoah/shenandoahStackChunkGCData.inline.hpp"
  79 #endif
  80 #if INCLUDE_ZGC
  81 #include "gc/z/zStackChunkGCData.inline.hpp"
  82 #endif
  83 #if INCLUDE_JFR
  84 #include "jfr/jfr.inline.hpp"
  85 #endif
  86 #ifdef COMPILER1
  87 #include "c1/c1_Runtime1.hpp"
  88 #endif
  89 #ifdef COMPILER2
  90 #include "opto/runtime.hpp"
  91 #endif
  92 
  93 /*
  94  * This file contains the implementation of continuation freezing (yield) and thawing (run).
  95  *
  96  * This code is very latency-critical and very hot. An ordinary and well-behaved server application
  97  * would likely call these operations many thousands of times per second second, on every core.
  98  *
  99  * Freeze might be called every time the application performs any I/O operation, every time it
 100  * acquires a j.u.c. lock, every time it takes a message from a queue, and thaw can be called
 101  * multiple times in each of those cases, as it is called by the return barrier, which may be
 102  * invoked on method return.
 103  *
 104  * The amortized budget for each of those two operations is ~100-150ns. That is why, for
 105  * example, every effort is made to avoid Java-VM transitions as much as possible.
 106  *
 107  * On the fast path, all frames are known to be compiled, and the chunk requires no barriers
 108  * and so frames simply copied, and the bottom-most one is patched.
 109  * On the slow path, internal pointers in interpreted frames are de/relativized to/from offsets
 110  * and absolute pointers, and barriers invoked.
 111  */
 112 
 113 /************************************************
 114 
 115 Thread-stack layout on freeze/thaw.
 116 See corresponding stack-chunk layout in instanceStackChunkKlass.hpp
 117 
 118             +----------------------------+
 119             |      .                     |
 120             |      .                     |
 121             |      .                     |
 122             |   carrier frames           |
 123             |                            |
 124             |----------------------------|
 125             |                            |
 126             |    Continuation.run        |
 127             |                            |
 128             |============================|
 129             |    enterSpecial frame      |
 130             |  pc                        |
 131             |  rbp                       |
 132             |  -----                     |
 133         ^   |  int argsize               | = ContinuationEntry
 134         |   |  oopDesc* cont             |
 135         |   |  oopDesc* chunk            |
 136         |   |  ContinuationEntry* parent |
 137         |   |  ...                       |
 138         |   |============================| <------ JavaThread::_cont_entry = entry->sp()
 139         |   |  ? alignment word ?        |
 140         |   |----------------------------| <--\
 141         |   |                            |    |
 142         |   |  ? caller stack args ?     |    |   argsize (might not be 2-word aligned) words
 143 Address |   |                            |    |   Caller is still in the chunk.
 144         |   |----------------------------|    |
 145         |   |  pc (? return barrier ?)   |    |  This pc contains the return barrier when the bottom-most frame
 146         |   |  rbp                       |    |  isn't the last one in the continuation.
 147         |   |                            |    |
 148         |   |    frame                   |    |
 149         |   |                            |    |
 150             +----------------------------|     \__ Continuation frames to be frozen/thawed
 151             |                            |     /
 152             |    frame                   |    |
 153             |                            |    |
 154             |----------------------------|    |
 155             |                            |    |
 156             |    frame                   |    |
 157             |                            |    |
 158             |----------------------------| <--/
 159             |                            |
 160             |    doYield/safepoint stub  | When preempting forcefully, we could have a safepoint stub
 161             |                            | instead of a doYield stub
 162             |============================| <- the sp passed to freeze
 163             |                            |
 164             |  Native freeze/thaw frames |
 165             |      .                     |
 166             |      .                     |
 167             |      .                     |
 168             +----------------------------+
 169 
 170 ************************************************/
 171 
 172 #define CONT_JFR false // emit low-level JFR events that count slow/fast path for continuation performance debugging only
 173 #if CONT_JFR
 174   #define CONT_JFR_ONLY(code) code
 175 #else
 176   #define CONT_JFR_ONLY(code)
 177 #endif
 178 
 179 // TODO: See AbstractAssembler::generate_stack_overflow_check,
 180 // Compile::bang_size_in_bytes(), m->as_SafePoint()->jvms()->interpreter_frame_size()
 181 // when we stack-bang, we need to update a thread field with the lowest (farthest) bang point.
 182 
 183 // Data invariants are defined by Continuation::debug_verify_continuation and Continuation::debug_verify_stack_chunk
 184 
 185 // Used to just annotatate cold/hot branches
 186 #define LIKELY(condition)   (condition)
 187 #define UNLIKELY(condition) (condition)
 188 
 189 // debugging functions
 190 #ifdef ASSERT
 191 extern "C" bool dbg_is_safe(const void* p, intptr_t errvalue); // address p is readable and *(intptr_t*)p != errvalue
 192 
 193 static void verify_continuation(oop continuation) { Continuation::debug_verify_continuation(continuation); }
 194 
 195 static void do_deopt_after_thaw(JavaThread* thread);
 196 static bool do_verify_after_thaw(JavaThread* thread, stackChunkOop chunk, outputStream* st);
 197 static bool verify_deopt_state(const frame& f);
 198 static void log_frames(JavaThread* thread);
 199 static void log_frames_after_thaw(JavaThread* thread, ContinuationWrapper& cont, intptr_t* sp);
 200 static void print_frame_layout(const frame& f, bool callee_complete, outputStream* st = tty);
 201 static void verify_frame_kind(frame& top, Continuation::preempt_kind preempt_kind, Method** m_ptr = nullptr, const char** code_name_ptr = nullptr, int* bci_ptr = nullptr, stackChunkOop chunk = nullptr);
 202 
 203 #define assert_pfl(p, ...) \
 204 do {                                           \
 205   if (!(p)) {                                  \
 206     JavaThread* t = JavaThread::active();      \
 207     if (t->has_last_Java_frame()) {            \
 208       tty->print_cr("assert(" #p ") failed:"); \
 209       t->print_frame_layout();                 \
 210     }                                          \
 211   }                                            \
 212   vmassert(p, __VA_ARGS__);                    \
 213 } while(0)
 214 
 215 #else
 216 static void verify_continuation(oop continuation) { }
 217 #define assert_pfl(p, ...)
 218 #endif
 219 
 220 static freeze_result is_pinned0(JavaThread* thread, oop cont_scope, bool safepoint);
 221 template<typename ConfigT, bool preempt> static inline freeze_result freeze_internal(JavaThread* current, intptr_t* const sp);
 222 
 223 static inline int prepare_thaw_internal(JavaThread* thread, bool return_barrier);
 224 template<typename ConfigT> static inline intptr_t* thaw_internal(JavaThread* thread, const Continuation::thaw_kind kind);
 225 
 226 // Entry point to freeze. Transitions are handled manually
 227 // Called from gen_continuation_yield() in sharedRuntime_<cpu>.cpp through Continuation::freeze_entry();
 228 template<typename ConfigT>
 229 static JRT_BLOCK_ENTRY(int, freeze(JavaThread* current, intptr_t* sp))
 230   assert(sp == current->frame_anchor()->last_Java_sp(), "");
 231 
 232   if (current->raw_cont_fastpath() > current->last_continuation()->entry_sp() || current->raw_cont_fastpath() < sp) {
 233     current->set_cont_fastpath(nullptr);
 234   }
 235 
 236   return checked_cast<int>(ConfigT::freeze(current, sp));
 237 JRT_END
 238 
 239 JRT_LEAF(int, Continuation::prepare_thaw(JavaThread* thread, bool return_barrier))
 240   return prepare_thaw_internal(thread, return_barrier);
 241 JRT_END
 242 
 243 template<typename ConfigT>
 244 static JRT_LEAF(intptr_t*, thaw(JavaThread* thread, int kind))
 245   // TODO: JRT_LEAF and NoHandleMark is problematic for JFR events.
 246   // vFrameStreamCommon allocates Handles in RegisterMap for continuations.
 247   // Also the preemption case with JVMTI events enabled might safepoint so
 248   // undo the NoSafepointVerifier here and rely on handling by ContinuationWrapper.
 249   // JRT_ENTRY instead?
 250   ResetNoHandleMark rnhm;
 251   DEBUG_ONLY(PauseNoSafepointVerifier pnsv(&__nsv);)
 252 
 253   // we might modify the code cache via BarrierSetNMethod::nmethod_entry_barrier
 254   MACOS_AARCH64_ONLY(ThreadWXEnable __wx(WXWrite, thread));
 255   return ConfigT::thaw(thread, (Continuation::thaw_kind)kind);
 256 JRT_END
 257 
 258 JVM_ENTRY(jint, CONT_isPinned0(JNIEnv* env, jobject cont_scope)) {
 259   JavaThread* thread = JavaThread::thread_from_jni_environment(env);
 260   return is_pinned0(thread, JNIHandles::resolve(cont_scope), false);
 261 }
 262 JVM_END
 263 
 264 ///////////
 265 
 266 enum class oop_kind { NARROW, WIDE };
 267 template <oop_kind oops, typename BarrierSetT>
 268 class Config {
 269 public:
 270   typedef Config<oops, BarrierSetT> SelfT;
 271   using OopT = std::conditional_t<oops == oop_kind::NARROW, narrowOop, oop>;
 272 
 273   static freeze_result freeze(JavaThread* thread, intptr_t* const sp) {
 274     freeze_result res = freeze_internal<SelfT, false>(thread, sp);
 275     JFR_ONLY(assert((res == freeze_ok) || (res == thread->last_freeze_fail_result()), "freeze failure not set"));
 276     return res;
 277   }
 278 
 279   static freeze_result freeze_preempt(JavaThread* thread, intptr_t* const sp) {
 280     return freeze_internal<SelfT, true>(thread, sp);
 281   }
 282 
 283   static intptr_t* thaw(JavaThread* thread, Continuation::thaw_kind kind) {
 284     return thaw_internal<SelfT>(thread, kind);
 285   }
 286 };
 287 
 288 #ifdef _WINDOWS
 289 static void map_stack_pages(JavaThread* thread, size_t size, address sp) {
 290   address new_sp = sp - size;
 291   address watermark = thread->stack_overflow_state()->shadow_zone_growth_watermark();
 292 
 293   if (new_sp < watermark) {
 294     size_t page_size = os::vm_page_size();
 295     address last_touched_page = watermark - StackOverflow::stack_shadow_zone_size();
 296     size_t pages_to_touch = align_up(watermark - new_sp, page_size) / page_size;
 297     while (pages_to_touch-- > 0) {
 298       last_touched_page -= page_size;
 299       *last_touched_page = 0;
 300     }
 301     thread->stack_overflow_state()->set_shadow_zone_growth_watermark(new_sp);
 302   }
 303 }
 304 #endif
 305 
 306 static bool stack_overflow_check(JavaThread* thread, size_t size, address sp) {
 307   const size_t page_size = os::vm_page_size();
 308   if (size > page_size) {
 309     if (sp - size < thread->stack_overflow_state()->shadow_zone_safe_limit()) {
 310       return false;
 311     }
 312     WINDOWS_ONLY(map_stack_pages(thread, size, sp));
 313   }
 314   return true;
 315 }
 316 
 317 #ifdef ASSERT
 318 static oop get_continuation(JavaThread* thread) {
 319   assert(thread != nullptr, "");
 320   assert(thread->threadObj() != nullptr, "");
 321   return java_lang_Thread::continuation(thread->threadObj());
 322 }
 323 #endif // ASSERT
 324 
 325 inline void clear_anchor(JavaThread* thread) {
 326   thread->frame_anchor()->clear();
 327 }
 328 
 329 static void set_anchor(JavaThread* thread, intptr_t* sp, address pc) {
 330   assert(pc != nullptr, "");
 331 
 332   JavaFrameAnchor* anchor = thread->frame_anchor();
 333   anchor->set_last_Java_sp(sp);
 334   anchor->set_last_Java_pc(pc);
 335   ContinuationHelper::set_anchor_pd(anchor, sp);
 336 
 337   assert(thread->has_last_Java_frame(), "");
 338   assert(thread->last_frame().cb() != nullptr, "");
 339 }
 340 
 341 static void set_anchor(JavaThread* thread, intptr_t* sp) {
 342   address pc = ContinuationHelper::return_address_at(
 343            sp - frame::sender_sp_ret_address_offset());
 344   set_anchor(thread, sp, pc);
 345 }
 346 
 347 static void set_anchor_to_entry(JavaThread* thread, ContinuationEntry* entry) {
 348   JavaFrameAnchor* anchor = thread->frame_anchor();
 349   anchor->set_last_Java_sp(entry->entry_sp());
 350   anchor->set_last_Java_pc(entry->entry_pc());
 351   ContinuationHelper::set_anchor_to_entry_pd(anchor, entry);
 352 
 353   assert(thread->has_last_Java_frame(), "");
 354   assert(thread->last_frame().cb() != nullptr, "");
 355 }
 356 
 357 #if CONT_JFR
 358 class FreezeThawJfrInfo : public StackObj {
 359   short _e_size;
 360   short _e_num_interpreted_frames;
 361  public:
 362 
 363   FreezeThawJfrInfo() : _e_size(0), _e_num_interpreted_frames(0) {}
 364   inline void record_interpreted_frame() { _e_num_interpreted_frames++; }
 365   inline void record_size_copied(int size) { _e_size += size << LogBytesPerWord; }
 366   template<typename Event> void post_jfr_event(Event *e, oop continuation, JavaThread* jt);
 367 };
 368 
 369 template<typename Event> void FreezeThawJfrInfo::post_jfr_event(Event* e, oop continuation, JavaThread* jt) {
 370   if (e->should_commit()) {
 371     log_develop_trace(continuations)("JFR event: iframes: %d size: %d", _e_num_interpreted_frames, _e_size);
 372     e->set_carrierThread(JFR_JVM_THREAD_ID(jt));
 373     e->set_continuationClass(continuation->klass());
 374     e->set_interpretedFrames(_e_num_interpreted_frames);
 375     e->set_size(_e_size);
 376     e->commit();
 377   }
 378 }
 379 #endif // CONT_JFR
 380 
 381 /////////////// FREEZE ////
 382 
 383 class FreezeBase : public StackObj {
 384 protected:
 385   JavaThread* const _thread;
 386   ContinuationWrapper& _cont;
 387   bool _barriers; // only set when we allocate a chunk
 388 
 389   intptr_t* _bottom_address;
 390 
 391   // Used for preemption only
 392   const bool _preempt;
 393   frame _last_frame;
 394 
 395   // Used to support freezing with held monitors
 396   int _monitors_in_lockstack;
 397 
 398   int _freeze_size; // total size of all frames plus metadata in words.
 399   int _total_align_size;
 400 
 401   intptr_t* _cont_stack_top;
 402   intptr_t* _cont_stack_bottom;
 403 
 404   CONT_JFR_ONLY(FreezeThawJfrInfo _jfr_info;)
 405 
 406 #ifdef ASSERT
 407   intptr_t* _orig_chunk_sp;
 408   int _fast_freeze_size;
 409   bool _empty;
 410 #endif
 411 
 412   JvmtiSampledObjectAllocEventCollector* _jvmti_event_collector;
 413 
 414   NOT_PRODUCT(int _frames;)
 415   DEBUG_ONLY(intptr_t* _last_write;)
 416 
 417   inline FreezeBase(JavaThread* thread, ContinuationWrapper& cont, intptr_t* sp, bool preempt);
 418 
 419 public:
 420   NOINLINE freeze_result freeze_slow();
 421   void freeze_fast_existing_chunk();
 422 
 423   CONT_JFR_ONLY(FreezeThawJfrInfo& jfr_info() { return _jfr_info; })
 424   void set_jvmti_event_collector(JvmtiSampledObjectAllocEventCollector* jsoaec) { _jvmti_event_collector = jsoaec; }
 425 
 426   inline int size_if_fast_freeze_available();
 427 
 428   inline frame& last_frame() { return _last_frame; }
 429 
 430 #ifdef ASSERT
 431   bool check_valid_fast_path();
 432 #endif
 433 
 434 protected:
 435   inline void init_rest();
 436   void throw_stack_overflow_on_humongous_chunk();
 437 
 438   // fast path
 439   inline void copy_to_chunk(intptr_t* from, intptr_t* to, int size);
 440   inline void unwind_frames();
 441   inline void patch_stack_pd(intptr_t* frame_sp, intptr_t* heap_sp);
 442 
 443   // slow path
 444   virtual stackChunkOop allocate_chunk_slow(size_t stack_size, int argsize_md) = 0;
 445 
 446   int cont_size() { return pointer_delta_as_int(_cont_stack_bottom, _cont_stack_top); }
 447 
 448 private:
 449   // slow path
 450   frame freeze_start_frame();
 451   frame freeze_start_frame_on_preempt();
 452   NOINLINE freeze_result recurse_freeze(frame& f, frame& caller, int callee_argsize, bool callee_interpreted, bool top);
 453   inline frame freeze_start_frame_yield_stub();
 454   template<typename FKind>
 455   inline freeze_result recurse_freeze_java_frame(const frame& f, frame& caller, int fsize, int argsize);
 456   inline void before_freeze_java_frame(const frame& f, const frame& caller, int fsize, int argsize, bool is_bottom_frame);
 457   inline void after_freeze_java_frame(const frame& hf, bool is_bottom_frame);
 458   freeze_result finalize_freeze(const frame& callee, frame& caller, int argsize);
 459   void patch(const frame& f, frame& hf, const frame& caller, bool is_bottom_frame);
 460   NOINLINE freeze_result recurse_freeze_interpreted_frame(frame& f, frame& caller, int callee_argsize, bool callee_interpreted);
 461   freeze_result recurse_freeze_compiled_frame(frame& f, frame& caller, int callee_argsize, bool callee_interpreted);
 462   NOINLINE freeze_result recurse_freeze_stub_frame(frame& f, frame& caller);
 463   NOINLINE freeze_result recurse_freeze_native_frame(frame& f, frame& caller);
 464   NOINLINE void finish_freeze(const frame& f, const frame& top);
 465 
 466   void freeze_lockstack(stackChunkOop chunk);
 467 
 468   inline bool stack_overflow();
 469 
 470   static frame sender(const frame& f) { return f.is_interpreted_frame() ? sender<ContinuationHelper::InterpretedFrame>(f)
 471                                                                         : sender<ContinuationHelper::NonInterpretedUnknownFrame>(f); }
 472   template<typename FKind> static inline frame sender(const frame& f);
 473   template<typename FKind> frame new_heap_frame(frame& f, frame& caller, int size_adjust = 0);
 474   inline void set_top_frame_metadata_pd(const frame& hf);
 475   inline void patch_pd(frame& callee, const frame& caller, bool is_bottom_frame);
 476   inline void patch_pd_unused(intptr_t* sp);
 477   void adjust_interpreted_frame_unextended_sp(frame& f);
 478   inline void prepare_freeze_interpreted_top_frame(frame& f);
 479   static inline void relativize_interpreted_frame_metadata(const frame& f, const frame& hf);
 480 
 481 protected:
 482   void freeze_fast_copy(stackChunkOop chunk, int chunk_start_sp CONT_JFR_ONLY(COMMA bool chunk_is_allocated));
 483   bool freeze_fast_new_chunk(stackChunkOop chunk);
 484 };
 485 
 486 template <typename ConfigT>
 487 class Freeze : public FreezeBase {
 488 private:
 489   stackChunkOop allocate_chunk(size_t stack_size, int argsize_md);
 490 
 491 public:
 492   inline Freeze(JavaThread* thread, ContinuationWrapper& cont, intptr_t* frame_sp, bool preempt)
 493     : FreezeBase(thread, cont, frame_sp, preempt) {}
 494 
 495   freeze_result try_freeze_fast();
 496 
 497 protected:
 498   virtual stackChunkOop allocate_chunk_slow(size_t stack_size, int argsize_md) override { return allocate_chunk(stack_size, argsize_md); }
 499 };
 500 
 501 FreezeBase::FreezeBase(JavaThread* thread, ContinuationWrapper& cont, intptr_t* frame_sp, bool preempt) :
 502     _thread(thread), _cont(cont), _barriers(false), _preempt(preempt), _last_frame(false /* no initialization */) {
 503   DEBUG_ONLY(_jvmti_event_collector = nullptr;)
 504 
 505   assert(_thread != nullptr, "");
 506   assert(_thread->last_continuation()->entry_sp() == _cont.entrySP(), "");
 507 
 508   DEBUG_ONLY(_cont.entry()->verify_cookie();)
 509 
 510   assert(!Interpreter::contains(_cont.entryPC()), "");
 511 
 512   _bottom_address = align_down(_cont.entrySP() - _cont.entry_frame_extension(), frame::frame_alignment);
 513 
 514   log_develop_trace(continuations)("bottom_address: " INTPTR_FORMAT " entrySP: " INTPTR_FORMAT " argsize: " PTR_FORMAT,
 515                 p2i(_bottom_address), p2i(_cont.entrySP()), (_cont.entrySP() - _bottom_address) << LogBytesPerWord);
 516   assert(_bottom_address != nullptr, "");
 517   assert(_bottom_address <= _cont.entrySP(), "");
 518   DEBUG_ONLY(_last_write = nullptr;)
 519 
 520   assert(_cont.chunk_invariant(), "");
 521   assert(!Interpreter::contains(_cont.entryPC()), "");
 522 #if defined(PPC64) && !defined(ZERO)
 523   static const int doYield_stub_frame_size = frame::native_abi_reg_args_size >> LogBytesPerWord;
 524 #elif defined(S390) && !defined(ZERO)
 525   static const int doYield_stub_frame_size = frame::z_abi_160_base_size >> LogBytesPerWord;
 526 #else
 527   static const int doYield_stub_frame_size = frame::metadata_words;
 528 #endif
 529   // With preemption doYield() might not have been resolved yet
 530   assert(_preempt || SharedRuntime::cont_doYield_stub()->frame_size() == doYield_stub_frame_size,
 531       "_preempt = %d, cont_doYield_stub()->frame_size() = %d, doYield_stub_frame_size = %d",
 532       (_preempt ? 1 : 0), SharedRuntime::cont_doYield_stub()->frame_size(), doYield_stub_frame_size);
 533 
 534   if (preempt) {
 535     _last_frame = _thread->last_frame();
 536   }
 537 
 538   // properties of the continuation on the stack; all sizes are in words
 539   _cont_stack_top    = frame_sp + (!preempt ? doYield_stub_frame_size : 0); // we don't freeze the doYield stub frame
 540   _cont_stack_bottom = _cont.entrySP() + (_cont.argsize() == 0 ? frame::metadata_words_at_top : 0)
 541       - ContinuationHelper::frame_align_words(_cont.argsize()); // see alignment in thaw
 542 
 543   log_develop_trace(continuations)("freeze size: %d argsize: %d top: " INTPTR_FORMAT " bottom: " INTPTR_FORMAT,
 544     cont_size(), _cont.argsize(), p2i(_cont_stack_top), p2i(_cont_stack_bottom));
 545   assert(cont_size() > 0, "");
 546 
 547   _monitors_in_lockstack = _thread->lock_stack().monitor_count();
 548 }
 549 
 550 void FreezeBase::init_rest() { // we want to postpone some initialization after chunk handling
 551   _freeze_size = 0;
 552   _total_align_size = 0;
 553   NOT_PRODUCT(_frames = 0;)
 554 }
 555 
 556 void FreezeBase::freeze_lockstack(stackChunkOop chunk) {
 557   assert(chunk->sp_address() - chunk->start_address() >= _monitors_in_lockstack, "no room for lockstack");
 558 
 559   _thread->lock_stack().move_to_address((oop*)chunk->start_address());
 560   chunk->set_lockstack_size(checked_cast<uint8_t>(_monitors_in_lockstack));
 561   chunk->set_has_lockstack(true);
 562 }
 563 
 564 void FreezeBase::copy_to_chunk(intptr_t* from, intptr_t* to, int size) {
 565   stackChunkOop chunk = _cont.tail();
 566   chunk->copy_from_stack_to_chunk(from, to, size);
 567   CONT_JFR_ONLY(_jfr_info.record_size_copied(size);)
 568 
 569 #ifdef ASSERT
 570   if (_last_write != nullptr) {
 571     assert(_last_write == to + size, "Missed a spot: _last_write: " INTPTR_FORMAT " to+size: " INTPTR_FORMAT
 572         " stack_size: %d _last_write offset: " PTR_FORMAT " to+size: " PTR_FORMAT, p2i(_last_write), p2i(to+size),
 573         chunk->stack_size(), _last_write-chunk->start_address(), to+size-chunk->start_address());
 574     _last_write = to;
 575   }
 576 #endif
 577 }
 578 
 579 static void assert_frames_in_continuation_are_safe(JavaThread* thread) {
 580 #ifdef ASSERT
 581   StackWatermark* watermark = StackWatermarkSet::get(thread, StackWatermarkKind::gc);
 582   if (watermark == nullptr) {
 583     return;
 584   }
 585   ContinuationEntry* ce = thread->last_continuation();
 586   RegisterMap map(thread,
 587                   RegisterMap::UpdateMap::include,
 588                   RegisterMap::ProcessFrames::skip,
 589                   RegisterMap::WalkContinuation::skip);
 590   map.set_include_argument_oops(false);
 591   for (frame f = thread->last_frame(); Continuation::is_frame_in_continuation(ce, f); f = f.sender(&map)) {
 592     watermark->assert_is_frame_safe(f);
 593   }
 594 #endif // ASSERT
 595 }
 596 
 597 // Called _after_ the last possible safepoint during the freeze operation (chunk allocation)
 598 void FreezeBase::unwind_frames() {
 599   ContinuationEntry* entry = _cont.entry();
 600   entry->flush_stack_processing(_thread);
 601   assert_frames_in_continuation_are_safe(_thread);
 602   JFR_ONLY(Jfr::check_and_process_sample_request(_thread);)
 603   set_anchor_to_entry(_thread, entry);
 604 }
 605 
 606 template <typename ConfigT>
 607 freeze_result Freeze<ConfigT>::try_freeze_fast() {
 608   assert(_thread->thread_state() == _thread_in_vm, "");
 609   assert(_thread->cont_fastpath(), "");
 610 
 611   DEBUG_ONLY(_fast_freeze_size = size_if_fast_freeze_available();)
 612   assert(_fast_freeze_size == 0, "");
 613 
 614   stackChunkOop chunk = allocate_chunk(cont_size() + frame::metadata_words + _monitors_in_lockstack, _cont.argsize() + frame::metadata_words_at_top);
 615   if (freeze_fast_new_chunk(chunk)) {
 616     return freeze_ok;
 617   }
 618   if (_thread->has_pending_exception()) {
 619     return freeze_exception;
 620   }
 621 
 622   // TODO R REMOVE when deopt change is fixed
 623   assert(!_thread->cont_fastpath() || _barriers, "");
 624   log_develop_trace(continuations)("-- RETRYING SLOW --");
 625   return freeze_slow();
 626 }
 627 
 628 // Returns size needed if the continuation fits, otherwise 0.
 629 int FreezeBase::size_if_fast_freeze_available() {
 630   stackChunkOop chunk = _cont.tail();
 631   if (chunk == nullptr || chunk->is_gc_mode() || chunk->requires_barriers() || chunk->has_mixed_frames()) {
 632     log_develop_trace(continuations)("chunk available %s", chunk == nullptr ? "no chunk" : "chunk requires barriers");
 633     return 0;
 634   }
 635 
 636   int total_size_needed = cont_size();
 637   const int chunk_sp = chunk->sp();
 638 
 639   // argsize can be nonzero if we have a caller, but the caller could be in a non-empty parent chunk,
 640   // so we subtract it only if we overlap with the caller, i.e. the current chunk isn't empty.
 641   // Consider leaving the chunk's argsize set when emptying it and removing the following branch,
 642   // although that would require changing stackChunkOopDesc::is_empty
 643   if (!chunk->is_empty()) {
 644     total_size_needed -= _cont.argsize() + frame::metadata_words_at_top;
 645   }
 646 
 647   total_size_needed += _monitors_in_lockstack;
 648 
 649   int chunk_free_room = chunk_sp - frame::metadata_words_at_bottom;
 650   bool available = chunk_free_room >= total_size_needed;
 651   log_develop_trace(continuations)("chunk available: %s size: %d argsize: %d top: " INTPTR_FORMAT " bottom: " INTPTR_FORMAT,
 652     available ? "yes" : "no" , total_size_needed, _cont.argsize(), p2i(_cont_stack_top), p2i(_cont_stack_bottom));
 653   return available ? total_size_needed : 0;
 654 }
 655 
 656 void FreezeBase::freeze_fast_existing_chunk() {
 657   stackChunkOop chunk = _cont.tail();
 658 
 659   DEBUG_ONLY(_fast_freeze_size = size_if_fast_freeze_available();)
 660   assert(_fast_freeze_size > 0, "");
 661 
 662   if (!chunk->is_empty()) { // we are copying into a non-empty chunk
 663     DEBUG_ONLY(_empty = false;)
 664     DEBUG_ONLY(_orig_chunk_sp = chunk->sp_address();)
 665 #ifdef ASSERT
 666     {
 667       intptr_t* retaddr_slot = (chunk->sp_address()
 668                                 - frame::sender_sp_ret_address_offset());
 669       assert(ContinuationHelper::return_address_at(retaddr_slot) == chunk->pc(),
 670              "unexpected saved return address");
 671     }
 672 #endif
 673 
 674     // the chunk's sp before the freeze, adjusted to point beyond the stack-passed arguments in the topmost frame
 675     // we overlap; we'll overwrite the chunk's top frame's callee arguments
 676     const int chunk_start_sp = chunk->sp() + _cont.argsize() + frame::metadata_words_at_top;
 677     assert(chunk_start_sp <= chunk->stack_size(), "sp not pointing into stack");
 678 
 679     // increase max_size by what we're freezing minus the overlap
 680     chunk->set_max_thawing_size(chunk->max_thawing_size() + cont_size() - _cont.argsize() - frame::metadata_words_at_top);
 681 
 682     intptr_t* const bottom_sp = _cont_stack_bottom - _cont.argsize() - frame::metadata_words_at_top;
 683     assert(bottom_sp == _bottom_address, "");
 684     // Because the chunk isn't empty, we know there's a caller in the chunk, therefore the bottom-most frame
 685     // should have a return barrier (installed back when we thawed it).
 686 #ifdef ASSERT
 687     {
 688       intptr_t* retaddr_slot = (bottom_sp
 689                                 - frame::sender_sp_ret_address_offset());
 690       assert(ContinuationHelper::return_address_at(retaddr_slot)
 691              == StubRoutines::cont_returnBarrier(),
 692              "should be the continuation return barrier");
 693     }
 694 #endif
 695     // We copy the fp from the chunk back to the stack because it contains some caller data,
 696     // including, possibly, an oop that might have gone stale since we thawed.
 697     patch_stack_pd(bottom_sp, chunk->sp_address());
 698     // we don't patch the return pc at this time, so as not to make the stack unwalkable for async walks
 699 
 700     freeze_fast_copy(chunk, chunk_start_sp CONT_JFR_ONLY(COMMA false));
 701   } else { // the chunk is empty
 702     const int chunk_start_sp = chunk->stack_size();
 703 
 704     DEBUG_ONLY(_empty = true;)
 705     DEBUG_ONLY(_orig_chunk_sp = chunk->start_address() + chunk_start_sp;)
 706 
 707     chunk->set_max_thawing_size(cont_size());
 708     chunk->set_bottom(chunk_start_sp - _cont.argsize() - frame::metadata_words_at_top);
 709     chunk->set_sp(chunk->bottom());
 710 
 711     freeze_fast_copy(chunk, chunk_start_sp CONT_JFR_ONLY(COMMA false));
 712   }
 713 }
 714 
 715 bool FreezeBase::freeze_fast_new_chunk(stackChunkOop chunk) {
 716   DEBUG_ONLY(_empty = true;)
 717 
 718   // Install new chunk
 719   _cont.set_tail(chunk);
 720 
 721   if (UNLIKELY(chunk == nullptr || !_thread->cont_fastpath() || _barriers)) { // OOME/probably humongous
 722     log_develop_trace(continuations)("Retrying slow. Barriers: %d", _barriers);
 723     return false;
 724   }
 725 
 726   chunk->set_max_thawing_size(cont_size());
 727 
 728   // in a fresh chunk, we freeze *with* the bottom-most frame's stack arguments.
 729   // They'll then be stored twice: in the chunk and in the parent chunk's top frame
 730   const int chunk_start_sp = cont_size() + frame::metadata_words + _monitors_in_lockstack;
 731   assert(chunk_start_sp == chunk->stack_size(), "");
 732 
 733   DEBUG_ONLY(_orig_chunk_sp = chunk->start_address() + chunk_start_sp;)
 734 
 735   freeze_fast_copy(chunk, chunk_start_sp CONT_JFR_ONLY(COMMA true));
 736 
 737   return true;
 738 }
 739 
 740 void FreezeBase::freeze_fast_copy(stackChunkOop chunk, int chunk_start_sp CONT_JFR_ONLY(COMMA bool chunk_is_allocated)) {
 741   assert(chunk != nullptr, "");
 742   assert(!chunk->has_mixed_frames(), "");
 743   assert(!chunk->is_gc_mode(), "");
 744   assert(!chunk->has_bitmap(), "");
 745   assert(!chunk->requires_barriers(), "");
 746   assert(chunk == _cont.tail(), "");
 747 
 748   // We unwind frames after the last safepoint so that the GC will have found the oops in the frames, but before
 749   // writing into the chunk. This is so that an asynchronous stack walk (not at a safepoint) that suspends us here
 750   // will either see no continuation on the stack, or a consistent chunk.
 751   unwind_frames();
 752 
 753   log_develop_trace(continuations)("freeze_fast start: chunk " INTPTR_FORMAT " size: %d orig sp: %d argsize: %d",
 754     p2i((oopDesc*)chunk), chunk->stack_size(), chunk_start_sp, _cont.argsize());
 755   assert(chunk_start_sp <= chunk->stack_size(), "");
 756   assert(chunk_start_sp >= cont_size(), "no room in the chunk");
 757 
 758   const int chunk_new_sp = chunk_start_sp - cont_size(); // the chunk's new sp, after freeze
 759   assert(!(_fast_freeze_size > 0) || (_orig_chunk_sp - (chunk->start_address() + chunk_new_sp)) == (_fast_freeze_size - _monitors_in_lockstack), "");
 760 
 761   intptr_t* chunk_top = chunk->start_address() + chunk_new_sp;
 762 #ifdef ASSERT
 763   if (!_empty) {
 764     intptr_t* retaddr_slot = (_orig_chunk_sp
 765                               - frame::sender_sp_ret_address_offset());
 766     assert(ContinuationHelper::return_address_at(retaddr_slot) == chunk->pc(),
 767            "unexpected saved return address");
 768   }
 769 #endif
 770 
 771   log_develop_trace(continuations)("freeze_fast start: " INTPTR_FORMAT " sp: %d chunk_top: " INTPTR_FORMAT,
 772                               p2i(chunk->start_address()), chunk_new_sp, p2i(chunk_top));
 773 
 774   int adjust = frame::metadata_words_at_bottom;
 775 #if INCLUDE_ASAN && defined(AARCH64)
 776   // Reading at offset frame::metadata_words_at_bottom from _cont_stack_top
 777   // will accesss memory at the callee frame, which on preemption cases will
 778   // be the VM native method being called. The Arm 64-bit ABI doesn't specify
 779   // a location where the frame record (returnpc+fp) has to be stored within
 780   // a stack frame, and GCC currently chooses to save it at the top of the
 781   // frame (lowest address). ASan treats this memory access in the callee as
 782   // an overflow access to one of the locals stored in that frame. For these
 783   // preemption cases we don't need to read these words anyways so we avoid it.
 784   if (_preempt) {
 785     adjust = 0;
 786   }
 787 #endif
 788   intptr_t* from = _cont_stack_top - adjust;
 789   intptr_t* to   = chunk_top - adjust;
 790   copy_to_chunk(from, to, cont_size() + adjust);
 791   // Because we're not patched yet, the chunk is now in a bad state
 792 
 793   // patch return pc of the bottom-most frozen frame (now in the chunk)
 794   // with the actual caller's return address
 795   intptr_t* chunk_bottom_retaddr_slot = (chunk_top + cont_size()
 796                                          - _cont.argsize()
 797                                          - frame::metadata_words_at_top
 798                                          - frame::sender_sp_ret_address_offset());
 799 #ifdef ASSERT
 800   if (!_empty) {
 801     assert(ContinuationHelper::return_address_at(chunk_bottom_retaddr_slot)
 802            == StubRoutines::cont_returnBarrier(),
 803            "should be the continuation return barrier");
 804   }
 805 #endif
 806   ContinuationHelper::patch_return_address_at(chunk_bottom_retaddr_slot,
 807                                               chunk->pc());
 808 
 809   // We're always writing to a young chunk, so the GC can't see it until the next safepoint.
 810   chunk->set_sp(chunk_new_sp);
 811 
 812   // set chunk->pc to the return address of the topmost frame in the chunk
 813   if (_preempt) {
 814     // On aarch64/riscv64, the return pc of the top frame won't necessarily be at sp[-1].
 815     // Also, on x64, if the top frame is the native wrapper frame, sp[-1] will not
 816     // be the pc we used when creating the oopmap. Get the top's frame last pc from
 817     // the anchor instead.
 818     address last_pc = _last_frame.pc();
 819     ContinuationHelper::patch_return_address_at(chunk_top - frame::sender_sp_ret_address_offset(), last_pc);
 820     chunk->set_pc(last_pc);
 821     // For stub/native frames the fp is not used while frozen, and will be constructed
 822     // again when thawing the frame (see ThawBase::handle_preempted_continuation). We
 823     // patch it with a special bad address to help with debugging, particularly when
 824     // inspecting frames and identifying invalid accesses.
 825     patch_pd_unused(chunk_top);
 826   } else {
 827     chunk->set_pc(ContinuationHelper::return_address_at(
 828                   _cont_stack_top - frame::sender_sp_ret_address_offset()));
 829   }
 830 
 831   if (_monitors_in_lockstack > 0) {
 832     freeze_lockstack(chunk);
 833   }
 834 
 835   _cont.write();
 836 
 837   log_develop_trace(continuations)("FREEZE CHUNK #" INTPTR_FORMAT " (young)", _cont.hash());
 838   LogTarget(Trace, continuations) lt;
 839   if (lt.develop_is_enabled()) {
 840     LogStream ls(lt);
 841     chunk->print_on(true, &ls);
 842   }
 843 
 844   // Verification
 845   assert(_cont.chunk_invariant(), "");
 846   chunk->verify();
 847 
 848 #if CONT_JFR
 849   EventContinuationFreezeFast e;
 850   if (e.should_commit()) {
 851     e.set_id(cast_from_oop<u8>(chunk));
 852     DEBUG_ONLY(e.set_allocate(chunk_is_allocated);)
 853     e.set_size(cont_size() << LogBytesPerWord);
 854     e.commit();
 855   }
 856 #endif
 857 }
 858 
 859 NOINLINE freeze_result FreezeBase::freeze_slow() {
 860 #ifdef ASSERT
 861   ResourceMark rm;
 862 #endif
 863 
 864   log_develop_trace(continuations)("freeze_slow  #" INTPTR_FORMAT, _cont.hash());
 865   assert(_thread->thread_state() == _thread_in_vm || _thread->thread_state() == _thread_blocked, "");
 866 
 867 #if CONT_JFR
 868   EventContinuationFreezeSlow e;
 869   if (e.should_commit()) {
 870     e.set_id(cast_from_oop<u8>(_cont.continuation()));
 871     e.commit();
 872   }
 873 #endif
 874 
 875   init_rest();
 876 
 877   HandleMark hm(Thread::current());
 878 
 879   frame f = freeze_start_frame();
 880 
 881   LogTarget(Debug, continuations) lt;
 882   if (lt.develop_is_enabled()) {
 883     LogStream ls(lt);
 884     f.print_on(&ls);
 885   }
 886 
 887   frame caller; // the frozen caller in the chunk
 888   freeze_result res = recurse_freeze(f, caller, 0, false, true);
 889 
 890   if (res == freeze_ok) {
 891     finish_freeze(f, caller);
 892     _cont.write();
 893   }
 894 
 895   return res;
 896 }
 897 
 898 frame FreezeBase::freeze_start_frame() {
 899   if (LIKELY(!_preempt)) {
 900     return freeze_start_frame_yield_stub();
 901   } else {
 902     return freeze_start_frame_on_preempt();
 903   }
 904 }
 905 
 906 frame FreezeBase::freeze_start_frame_yield_stub() {
 907   frame f = _thread->last_frame();
 908   assert(SharedRuntime::cont_doYield_stub()->contains(f.pc()), "must be");
 909   f = sender<ContinuationHelper::NonInterpretedUnknownFrame>(f);
 910   assert(Continuation::is_frame_in_continuation(_thread->last_continuation(), f), "");
 911   return f;
 912 }
 913 
 914 frame FreezeBase::freeze_start_frame_on_preempt() {
 915   assert(_last_frame.sp() == _thread->last_frame().sp(), "_last_frame should be already initialized");
 916   assert(Continuation::is_frame_in_continuation(_thread->last_continuation(), _last_frame), "");
 917   return _last_frame;
 918 }
 919 
 920 // The parameter callee_argsize includes metadata that has to be part of caller/callee overlap.
 921 NOINLINE freeze_result FreezeBase::recurse_freeze(frame& f, frame& caller, int callee_argsize, bool callee_interpreted, bool top) {
 922   assert(f.unextended_sp() < _bottom_address, ""); // see recurse_freeze_java_frame
 923   assert(f.is_interpreted_frame() || ((top && _preempt) == ContinuationHelper::Frame::is_stub(f.cb()))
 924          || ((top && _preempt) == f.is_native_frame()), "");
 925 
 926   if (stack_overflow()) {
 927     return freeze_exception;
 928   }
 929 
 930   if (f.is_compiled_frame()) {
 931     if (UNLIKELY(f.oop_map() == nullptr)) {
 932       // special native frame
 933       return freeze_pinned_native;
 934     }
 935     return recurse_freeze_compiled_frame(f, caller, callee_argsize, callee_interpreted);
 936   } else if (f.is_interpreted_frame()) {
 937     assert(!f.interpreter_frame_method()->is_native() || (top && _preempt), "");
 938     return recurse_freeze_interpreted_frame(f, caller, callee_argsize, callee_interpreted);
 939   } else if (top && _preempt) {
 940     assert(f.is_native_frame() || f.is_runtime_frame(), "");
 941     return f.is_native_frame() ? recurse_freeze_native_frame(f, caller) : recurse_freeze_stub_frame(f, caller);
 942   } else {
 943     // Frame can't be frozen. Most likely the call_stub or upcall_stub
 944     // which indicates there are further natives frames up the stack.
 945     return freeze_pinned_native;
 946   }
 947 }
 948 
 949 // The parameter callee_argsize includes metadata that has to be part of caller/callee overlap.
 950 // See also StackChunkFrameStream<frame_kind>::frame_size()
 951 template<typename FKind>
 952 inline freeze_result FreezeBase::recurse_freeze_java_frame(const frame& f, frame& caller, int fsize, int argsize) {
 953   assert(FKind::is_instance(f), "");
 954 
 955   assert(fsize > 0, "");
 956   assert(argsize >= 0, "");
 957   _freeze_size += fsize;
 958   NOT_PRODUCT(_frames++;)
 959 
 960   assert(FKind::frame_bottom(f) <= _bottom_address, "");
 961 
 962   // We don't use FKind::frame_bottom(f) == _bottom_address because on x64 there's sometimes an extra word between
 963   // enterSpecial and an interpreted frame
 964   if (FKind::frame_bottom(f) >= _bottom_address - 1) {
 965     return finalize_freeze(f, caller, argsize); // recursion end
 966   } else {
 967     frame senderf = sender<FKind>(f);
 968     assert(FKind::interpreted || senderf.sp() == senderf.unextended_sp(), "");
 969     freeze_result result = recurse_freeze(senderf, caller, argsize, FKind::interpreted, false); // recursive call
 970     return result;
 971   }
 972 }
 973 
 974 inline void FreezeBase::before_freeze_java_frame(const frame& f, const frame& caller, int fsize, int argsize, bool is_bottom_frame) {
 975   LogTarget(Trace, continuations) lt;
 976   if (lt.develop_is_enabled()) {
 977     LogStream ls(lt);
 978     ls.print_cr("======== FREEZING FRAME interpreted: %d bottom: %d", f.is_interpreted_frame(), is_bottom_frame);
 979     ls.print_cr("fsize: %d argsize: %d", fsize, argsize);
 980     f.print_value_on(&ls);
 981   }
 982   assert(caller.is_interpreted_frame() == Interpreter::contains(caller.pc()), "");
 983 }
 984 
 985 inline void FreezeBase::after_freeze_java_frame(const frame& hf, bool is_bottom_frame) {
 986   LogTarget(Trace, continuations) lt;
 987   if (lt.develop_is_enabled()) {
 988     LogStream ls(lt);
 989     DEBUG_ONLY(hf.print_value_on(&ls);)
 990     assert(hf.is_heap_frame(), "should be");
 991     DEBUG_ONLY(print_frame_layout(hf, false, &ls);)
 992     if (is_bottom_frame) {
 993       ls.print_cr("bottom h-frame:");
 994       hf.print_on(&ls);
 995     }
 996   }
 997 }
 998 
 999 // The parameter argsize_md includes metadata that has to be part of caller/callee overlap.
1000 // See also StackChunkFrameStream<frame_kind>::frame_size()
1001 freeze_result FreezeBase::finalize_freeze(const frame& callee, frame& caller, int argsize_md) {
1002   int argsize = argsize_md - frame::metadata_words_at_top;
1003   assert(callee.is_interpreted_frame()
1004     || ContinuationHelper::Frame::is_stub(callee.cb())
1005     || callee.cb()->as_nmethod()->is_osr_method()
1006     || argsize == _cont.argsize(), "argsize: %d cont.argsize: %d", argsize, _cont.argsize());
1007   log_develop_trace(continuations)("bottom: " INTPTR_FORMAT " count %d size: %d argsize: %d",
1008     p2i(_bottom_address), _frames, _freeze_size << LogBytesPerWord, argsize);
1009 
1010   LogTarget(Trace, continuations) lt;
1011 
1012 #ifdef ASSERT
1013   bool empty = _cont.is_empty();
1014   log_develop_trace(continuations)("empty: %d", empty);
1015 #endif
1016 
1017   stackChunkOop chunk = _cont.tail();
1018 
1019   assert(chunk == nullptr || (chunk->max_thawing_size() == 0) == chunk->is_empty(), "");
1020 
1021   _freeze_size += frame::metadata_words; // for top frame's metadata
1022 
1023   int overlap = 0; // the args overlap the caller -- if there is one in this chunk and is of the same kind
1024   int unextended_sp = -1;
1025   if (chunk != nullptr) {
1026     if (!chunk->is_empty()) {
1027       StackChunkFrameStream<ChunkFrames::Mixed> last(chunk);
1028       unextended_sp = chunk->to_offset(StackChunkFrameStream<ChunkFrames::Mixed>(chunk).unextended_sp());
1029       bool top_interpreted = Interpreter::contains(chunk->pc());
1030       if (callee.is_interpreted_frame() == top_interpreted) {
1031         overlap = argsize_md;
1032       }
1033     } else {
1034       unextended_sp = chunk->stack_size() - frame::metadata_words_at_top;
1035     }
1036   }
1037 
1038   log_develop_trace(continuations)("finalize _size: %d overlap: %d unextended_sp: %d", _freeze_size, overlap, unextended_sp);
1039 
1040   _freeze_size -= overlap;
1041   assert(_freeze_size >= 0, "");
1042 
1043   assert(chunk == nullptr || chunk->is_empty()
1044           || unextended_sp == chunk->to_offset(StackChunkFrameStream<ChunkFrames::Mixed>(chunk).unextended_sp()), "");
1045   assert(chunk != nullptr || unextended_sp < _freeze_size, "");
1046 
1047   _freeze_size += _monitors_in_lockstack;
1048 
1049   // _barriers can be set to true by an allocation in freeze_fast, in which case the chunk is available
1050   bool allocated_old_in_freeze_fast = _barriers;
1051   assert(!allocated_old_in_freeze_fast || (unextended_sp >= _freeze_size && chunk->is_empty()),
1052     "Chunk allocated in freeze_fast is of insufficient size "
1053     "unextended_sp: %d size: %d is_empty: %d", unextended_sp, _freeze_size, chunk->is_empty());
1054   assert(!allocated_old_in_freeze_fast || (!UseZGC && !UseG1GC), "Unexpected allocation");
1055 
1056   DEBUG_ONLY(bool empty_chunk = true);
1057   if (unextended_sp < _freeze_size || chunk->is_gc_mode() || (!allocated_old_in_freeze_fast && chunk->requires_barriers())) {
1058     // ALLOCATE NEW CHUNK
1059 
1060     if (lt.develop_is_enabled()) {
1061       LogStream ls(lt);
1062       if (chunk == nullptr) {
1063         ls.print_cr("no chunk");
1064       } else {
1065         ls.print_cr("chunk barriers: %d _size: %d free size: %d",
1066           chunk->requires_barriers(), _freeze_size, chunk->sp() - frame::metadata_words);
1067         chunk->print_on(&ls);
1068       }
1069     }
1070 
1071     _freeze_size += overlap; // we're allocating a new chunk, so no overlap
1072     // overlap = 0;
1073 
1074     chunk = allocate_chunk_slow(_freeze_size, argsize_md);
1075     if (chunk == nullptr) {
1076       return freeze_exception;
1077     }
1078 
1079     // Install new chunk
1080     _cont.set_tail(chunk);
1081     assert(chunk->is_empty(), "");
1082   } else {
1083     // REUSE EXISTING CHUNK
1084     log_develop_trace(continuations)("Reusing chunk mixed: %d empty: %d", chunk->has_mixed_frames(), chunk->is_empty());
1085     if (chunk->is_empty()) {
1086       int sp = chunk->stack_size() - argsize_md;
1087       chunk->set_sp(sp);
1088       chunk->set_bottom(sp);
1089       _freeze_size += overlap;
1090       assert(chunk->max_thawing_size() == 0, "");
1091     } DEBUG_ONLY(else empty_chunk = false;)
1092   }
1093   assert(!chunk->is_gc_mode(), "");
1094   assert(!chunk->has_bitmap(), "");
1095   chunk->set_has_mixed_frames(true);
1096 
1097   assert(chunk->requires_barriers() == _barriers, "");
1098   assert(!_barriers || chunk->is_empty(), "");
1099 
1100   assert(!chunk->is_empty() || StackChunkFrameStream<ChunkFrames::Mixed>(chunk).is_done(), "");
1101   assert(!chunk->is_empty() || StackChunkFrameStream<ChunkFrames::Mixed>(chunk).to_frame().is_empty(), "");
1102 
1103   if (_preempt) {
1104     frame top_frame = _thread->last_frame();
1105     if (top_frame.is_interpreted_frame()) {
1106       // Some platforms do not save the last_sp in the top interpreter frame on VM calls.
1107       // We need it so that on resume we can restore the sp to the right place, since
1108       // thawing might add an alignment word to the expression stack (see finish_thaw()).
1109       // We do it now that we know freezing will be successful.
1110       prepare_freeze_interpreted_top_frame(top_frame);
1111     }
1112 
1113     // Do this now so should_process_args_at_top() is set before calling finish_freeze
1114     // in case we might need to apply GC barriers to frames in this stackChunk.
1115     if (_thread->at_preemptable_init()) {
1116       assert(top_frame.is_interpreted_frame(), "only InterpreterRuntime::_new/resolve_from_cache allowed");
1117       chunk->set_at_klass_init(true);
1118       methodHandle m(_thread, top_frame.interpreter_frame_method());
1119       Bytecode_invoke call = Bytecode_invoke_check(m, top_frame.interpreter_frame_bci());
1120       assert(!call.is_valid() || call.is_invokestatic(), "only invokestatic allowed");
1121       if (call.is_invokestatic() && call.size_of_parameters() > 0) {
1122         assert(top_frame.interpreter_frame_expression_stack_size() > 0, "should have parameters in exp stack");
1123         chunk->set_has_args_at_top(true);
1124       }
1125     }
1126   }
1127 
1128   // We unwind frames after the last safepoint so that the GC will have found the oops in the frames, but before
1129   // writing into the chunk. This is so that an asynchronous stack walk (not at a safepoint) that suspends us here
1130   // will either see no continuation or a consistent chunk.
1131   unwind_frames();
1132 
1133   chunk->set_max_thawing_size(chunk->max_thawing_size() + _freeze_size - _monitors_in_lockstack - frame::metadata_words);
1134 
1135   if (lt.develop_is_enabled()) {
1136     LogStream ls(lt);
1137     ls.print_cr("top chunk:");
1138     chunk->print_on(&ls);
1139   }
1140 
1141   if (_monitors_in_lockstack > 0) {
1142     freeze_lockstack(chunk);
1143   }
1144 
1145   // The topmost existing frame in the chunk; or an empty frame if the chunk is empty
1146   caller = StackChunkFrameStream<ChunkFrames::Mixed>(chunk).to_frame();
1147 
1148   DEBUG_ONLY(_last_write = caller.unextended_sp() + (empty_chunk ? argsize_md : overlap);)
1149 
1150   assert(chunk->is_in_chunk(_last_write - _freeze_size),
1151     "last_write-size: " INTPTR_FORMAT " start: " INTPTR_FORMAT, p2i(_last_write-_freeze_size), p2i(chunk->start_address()));
1152 #ifdef ASSERT
1153   if (lt.develop_is_enabled()) {
1154     LogStream ls(lt);
1155     ls.print_cr("top hframe before (freeze):");
1156     assert(caller.is_heap_frame(), "should be");
1157     caller.print_on(&ls);
1158   }
1159 
1160   assert(!empty || Continuation::is_continuation_entry_frame(callee, nullptr), "");
1161 
1162   frame entry = sender(callee);
1163 
1164   assert((!empty && Continuation::is_return_barrier_entry(entry.pc())) || (empty && Continuation::is_continuation_enterSpecial(entry)), "");
1165   assert(callee.is_interpreted_frame() || entry.sp() == entry.unextended_sp(), "");
1166 #endif
1167 
1168   return freeze_ok_bottom;
1169 }
1170 
1171 // After freezing a frame we need to possibly adjust some values related to the caller frame.
1172 void FreezeBase::patch(const frame& f, frame& hf, const frame& caller, bool is_bottom_frame) {
1173   if (is_bottom_frame) {
1174     // If we're the bottom frame, we need to replace the return barrier with the real
1175     // caller's pc.
1176     address last_pc = caller.pc();
1177     assert((last_pc == nullptr) == _cont.tail()->is_empty(), "");
1178     ContinuationHelper::Frame::patch_pc(caller, last_pc);
1179   } else {
1180     assert(!caller.is_empty(), "");
1181   }
1182 
1183   patch_pd(hf, caller, is_bottom_frame);
1184 
1185   if (f.is_interpreted_frame()) {
1186     assert(hf.is_heap_frame(), "should be");
1187     ContinuationHelper::InterpretedFrame::patch_sender_sp(hf, caller);
1188   }
1189 
1190 #ifdef ASSERT
1191   if (hf.is_compiled_frame()) {
1192     if (f.is_deoptimized_frame()) { // TODO DEOPT: long term solution: unroll on freeze and patch pc
1193       log_develop_trace(continuations)("Freezing deoptimized frame");
1194       assert(f.cb()->as_nmethod()->is_deopt_pc(f.raw_pc()), "");
1195       assert(f.cb()->as_nmethod()->is_deopt_pc(ContinuationHelper::Frame::real_pc(f)), "");
1196     }
1197   }
1198 #endif
1199 }
1200 
1201 #ifdef ASSERT
1202 static void verify_frame_top(const frame& f, intptr_t* top) {
1203   ResourceMark rm;
1204   InterpreterOopMap mask;
1205   f.interpreted_frame_oop_map(&mask);
1206   assert(top <= ContinuationHelper::InterpretedFrame::frame_top(f, &mask),
1207          "frame_top: " INTPTR_FORMAT " Interpreted::frame_top: " INTPTR_FORMAT,
1208            p2i(top), p2i(ContinuationHelper::InterpretedFrame::frame_top(f, &mask)));
1209 }
1210 #endif // ASSERT
1211 
1212 // The parameter callee_argsize includes metadata that has to be part of caller/callee overlap.
1213 // See also StackChunkFrameStream<frame_kind>::frame_size()
1214 NOINLINE freeze_result FreezeBase::recurse_freeze_interpreted_frame(frame& f, frame& caller,
1215                                                                     int callee_argsize /* incl. metadata */,
1216                                                                     bool callee_interpreted) {
1217   adjust_interpreted_frame_unextended_sp(f);
1218 
1219   // The frame's top never includes the stack arguments to the callee
1220   intptr_t* const stack_frame_top = ContinuationHelper::InterpretedFrame::frame_top(f, callee_argsize, callee_interpreted);
1221   intptr_t* const stack_frame_bottom = ContinuationHelper::InterpretedFrame::frame_bottom(f);
1222   const int fsize = pointer_delta_as_int(stack_frame_bottom, stack_frame_top);
1223 
1224   DEBUG_ONLY(verify_frame_top(f, stack_frame_top));
1225 
1226   Method* frame_method = ContinuationHelper::Frame::frame_method(f);
1227   // including metadata between f and its args
1228   const int argsize = ContinuationHelper::InterpretedFrame::stack_argsize(f) + frame::metadata_words_at_top;
1229 
1230   log_develop_trace(continuations)("recurse_freeze_interpreted_frame %s _size: %d fsize: %d argsize: %d callee_interpreted: %d",
1231     frame_method->name_and_sig_as_C_string(), _freeze_size, fsize, argsize, callee_interpreted);
1232   // we'd rather not yield inside methods annotated with @JvmtiMountTransition
1233   assert(!ContinuationHelper::Frame::frame_method(f)->jvmti_mount_transition(), "");
1234 
1235   freeze_result result = recurse_freeze_java_frame<ContinuationHelper::InterpretedFrame>(f, caller, fsize, argsize);
1236   if (UNLIKELY(result > freeze_ok_bottom)) {
1237     return result;
1238   }
1239 
1240   bool is_bottom_frame = result == freeze_ok_bottom;
1241   assert(!caller.is_empty() || is_bottom_frame, "");
1242 
1243   DEBUG_ONLY(before_freeze_java_frame(f, caller, fsize, 0, is_bottom_frame);)
1244 
1245   frame hf = new_heap_frame<ContinuationHelper::InterpretedFrame>(f, caller);
1246   _total_align_size += frame::align_wiggle; // add alignment room for internal interpreted frame alignment on AArch64/PPC64
1247 
1248   intptr_t* heap_frame_top = ContinuationHelper::InterpretedFrame::frame_top(hf, callee_argsize, callee_interpreted);
1249   intptr_t* heap_frame_bottom = ContinuationHelper::InterpretedFrame::frame_bottom(hf);
1250   assert(heap_frame_bottom == heap_frame_top + fsize, "");
1251 
1252   // Some architectures (like AArch64/PPC64/RISC-V) add padding between the locals and the fixed_frame to keep the fp 16-byte-aligned.
1253   // On those architectures we freeze the padding in order to keep the same fp-relative offsets in the fixed_frame.
1254   copy_to_chunk(stack_frame_top, heap_frame_top, fsize);
1255   assert(!is_bottom_frame || !caller.is_interpreted_frame() || (heap_frame_top + fsize) == (caller.unextended_sp() + argsize), "");
1256 
1257   relativize_interpreted_frame_metadata(f, hf);
1258 
1259   patch(f, hf, caller, is_bottom_frame);
1260 
1261   CONT_JFR_ONLY(_jfr_info.record_interpreted_frame();)
1262   DEBUG_ONLY(after_freeze_java_frame(hf, is_bottom_frame);)
1263   caller = hf;
1264 
1265   // Mark frame_method's GC epoch for class redefinition on_stack calculation.
1266   frame_method->record_gc_epoch();
1267 
1268   return freeze_ok;
1269 }
1270 
1271 // The parameter callee_argsize includes metadata that has to be part of caller/callee overlap.
1272 // See also StackChunkFrameStream<frame_kind>::frame_size()
1273 freeze_result FreezeBase::recurse_freeze_compiled_frame(frame& f, frame& caller,
1274                                                         int callee_argsize /* incl. metadata */,
1275                                                         bool callee_interpreted) {
1276   // The frame's top never includes the stack arguments to the callee
1277   intptr_t* const stack_frame_top = ContinuationHelper::CompiledFrame::frame_top(f, callee_argsize, callee_interpreted);
1278   intptr_t* const stack_frame_bottom = ContinuationHelper::CompiledFrame::frame_bottom(f);
1279   // including metadata between f and its stackargs
1280   int argsize = ContinuationHelper::CompiledFrame::stack_argsize(f) + frame::metadata_words_at_top;
1281   int fsize = pointer_delta_as_int(stack_frame_bottom + argsize, stack_frame_top);
1282 
1283   int real_frame_size = 0;
1284   bool augmented = f.was_augmented_on_entry(real_frame_size);
1285   if (augmented) {
1286     assert(f.cb()->as_nmethod()->is_compiled_by_c2(), "should be c2 compiled");
1287     // The args reside inside the frame so clear argsize. If the caller is compiled,
1288     // this will cause the stack arguments passed by the caller to be freezed when
1289     // freezing the caller frame itself. If the caller is interpreted this will have
1290     // the effect of discarding the arg area created in the i2c stub.
1291     argsize = 0;
1292     fsize = real_frame_size - (callee_interpreted ? 0 : callee_argsize);
1293   }
1294 
1295   log_develop_trace(continuations)("recurse_freeze_compiled_frame %s _size: %d fsize: %d argsize: %d augmented: %d",
1296                              ContinuationHelper::Frame::frame_method(f) != nullptr ?
1297                              ContinuationHelper::Frame::frame_method(f)->name_and_sig_as_C_string() : "",
1298                              _freeze_size, fsize, argsize, augmented);
1299   // we'd rather not yield inside methods annotated with @JvmtiMountTransition
1300   assert(!ContinuationHelper::Frame::frame_method(f)->jvmti_mount_transition(), "");
1301 
1302   freeze_result result = recurse_freeze_java_frame<ContinuationHelper::CompiledFrame>(f, caller, fsize, argsize);
1303   if (UNLIKELY(result > freeze_ok_bottom)) {
1304     return result;
1305   }
1306 
1307   bool is_bottom_frame = result == freeze_ok_bottom;
1308   assert(!caller.is_empty() || is_bottom_frame, "");
1309   assert(!is_bottom_frame || !augmented, "thaw extended frame without caller?");
1310 
1311   DEBUG_ONLY(before_freeze_java_frame(f, caller, fsize, argsize, is_bottom_frame);)
1312 
1313   frame hf = new_heap_frame<ContinuationHelper::CompiledFrame>(f, caller, augmented ? real_frame_size - f.cb()->as_nmethod()->frame_size() : 0);
1314 
1315   intptr_t* heap_frame_top = ContinuationHelper::CompiledFrame::frame_top(hf, callee_argsize, callee_interpreted);
1316 
1317   copy_to_chunk(stack_frame_top, heap_frame_top, fsize);
1318   assert(!is_bottom_frame || !caller.is_compiled_frame() || (heap_frame_top + fsize) == (caller.unextended_sp() + argsize), "");
1319 
1320   if (caller.is_interpreted_frame()) {
1321     // When thawing the frame we might need to add alignment (see Thaw::align)
1322     _total_align_size += frame::align_wiggle;
1323   }
1324 
1325   patch(f, hf, caller, is_bottom_frame);
1326 
1327   assert(is_bottom_frame || Interpreter::contains(ContinuationHelper::CompiledFrame::real_pc(caller)) == caller.is_interpreted_frame(), "");
1328 
1329   DEBUG_ONLY(after_freeze_java_frame(hf, is_bottom_frame);)
1330   caller = hf;
1331   return freeze_ok;
1332 }
1333 
1334 NOINLINE freeze_result FreezeBase::recurse_freeze_stub_frame(frame& f, frame& caller) {
1335   DEBUG_ONLY(frame fsender = sender(f);)
1336   assert(fsender.is_compiled_frame(), "sender should be compiled frame");
1337 
1338   intptr_t* const stack_frame_top = ContinuationHelper::StubFrame::frame_top(f);
1339   const int fsize = f.cb()->frame_size();
1340 
1341   log_develop_trace(continuations)("recurse_freeze_stub_frame %s _size: %d fsize: %d :: " INTPTR_FORMAT " - " INTPTR_FORMAT,
1342     f.cb()->name(), _freeze_size, fsize, p2i(stack_frame_top), p2i(stack_frame_top+fsize));
1343 
1344   freeze_result result = recurse_freeze_java_frame<ContinuationHelper::StubFrame>(f, caller, fsize, 0);
1345   if (UNLIKELY(result > freeze_ok_bottom)) {
1346     return result;
1347   }
1348 
1349   assert(result == freeze_ok, "should have caller");
1350   DEBUG_ONLY(before_freeze_java_frame(f, caller, fsize, 0, false /*is_bottom_frame*/);)
1351 
1352   frame hf = new_heap_frame<ContinuationHelper::StubFrame>(f, caller);
1353   intptr_t* heap_frame_top = ContinuationHelper::StubFrame::frame_top(hf);
1354 
1355   copy_to_chunk(stack_frame_top, heap_frame_top, fsize);
1356 
1357   patch(f, hf, caller, false /*is_bottom_frame*/);
1358 
1359   DEBUG_ONLY(after_freeze_java_frame(hf, false /*is_bottom_frame*/);)
1360 
1361   caller = hf;
1362   return freeze_ok;
1363 }
1364 
1365 NOINLINE freeze_result FreezeBase::recurse_freeze_native_frame(frame& f, frame& caller) {
1366   if (!f.cb()->as_nmethod()->method()->is_object_wait0()) {
1367     assert(f.cb()->as_nmethod()->method()->is_synchronized(), "");
1368     // Synchronized native method case. Unlike the interpreter native wrapper, the compiled
1369     // native wrapper tries to acquire the monitor after marshalling the arguments from the
1370     // caller into the native convention. This is so that we have a valid oopMap in case of
1371     // having to block in the slow path. But that would require freezing those registers too
1372     // and then fixing them back on thaw in case of oops. To avoid complicating things and
1373     // given that this would be a rare case anyways just pin the vthread to the carrier.
1374     return freeze_pinned_native;
1375   }
1376 
1377   intptr_t* const stack_frame_top = ContinuationHelper::NativeFrame::frame_top(f);
1378   // There are no stackargs but argsize must include the metadata
1379   const int argsize = frame::metadata_words_at_top;
1380   const int fsize = f.cb()->frame_size() + argsize;
1381 
1382   log_develop_trace(continuations)("recurse_freeze_native_frame %s _size: %d fsize: %d :: " INTPTR_FORMAT " - " INTPTR_FORMAT,
1383     f.cb()->name(), _freeze_size, fsize, p2i(stack_frame_top), p2i(stack_frame_top+fsize));
1384 
1385   freeze_result result = recurse_freeze_java_frame<ContinuationHelper::NativeFrame>(f, caller, fsize, argsize);
1386   if (UNLIKELY(result > freeze_ok_bottom)) {
1387     return result;
1388   }
1389 
1390   assert(result == freeze_ok, "should have caller frame");
1391   DEBUG_ONLY(before_freeze_java_frame(f, caller, fsize, argsize, false /* is_bottom_frame */);)
1392 
1393   frame hf = new_heap_frame<ContinuationHelper::NativeFrame>(f, caller);
1394   intptr_t* heap_frame_top = ContinuationHelper::NativeFrame::frame_top(hf);
1395 
1396   copy_to_chunk(stack_frame_top, heap_frame_top, fsize);
1397 
1398   if (caller.is_interpreted_frame()) {
1399     // When thawing the frame we might need to add alignment (see Thaw::align)
1400     _total_align_size += frame::align_wiggle;
1401   }
1402 
1403   patch(f, hf, caller, false /* is_bottom_frame */);
1404 
1405   DEBUG_ONLY(after_freeze_java_frame(hf, false /* is_bottom_frame */);)
1406 
1407   caller = hf;
1408   return freeze_ok;
1409 }
1410 
1411 NOINLINE void FreezeBase::finish_freeze(const frame& f, const frame& top) {
1412   stackChunkOop chunk = _cont.tail();
1413 
1414   LogTarget(Trace, continuations) lt;
1415   if (lt.develop_is_enabled()) {
1416     LogStream ls(lt);
1417     assert(top.is_heap_frame(), "should be");
1418     top.print_on(&ls);
1419   }
1420 
1421   set_top_frame_metadata_pd(top);
1422 
1423   chunk->set_sp(chunk->to_offset(top.sp()));
1424   chunk->set_pc(top.pc());
1425 
1426   chunk->set_max_thawing_size(chunk->max_thawing_size() + _total_align_size);
1427 
1428   assert(chunk->sp_address() - chunk->start_address() >= _monitors_in_lockstack, "clash with lockstack");
1429 
1430   // At this point the chunk is consistent
1431 
1432   if (UNLIKELY(_barriers)) {
1433     log_develop_trace(continuations)("do barriers on old chunk");
1434     // Serial and Parallel GC can allocate objects directly into the old generation.
1435     // Then we want to relativize the derived pointers eagerly so that
1436     // old chunks are all in GC mode.
1437     assert(!UseG1GC, "G1 can not deal with allocating outside of eden");
1438     assert(!UseZGC, "ZGC can not deal with allocating chunks visible to marking");
1439     if (UseShenandoahGC) {
1440       _cont.tail()->relativize_derived_pointers_concurrently();
1441     } else {
1442       ContinuationGCSupport::transform_stack_chunk(_cont.tail());
1443     }
1444     // For objects in the old generation we must maintain the remembered set
1445     _cont.tail()->do_barriers<stackChunkOopDesc::BarrierType::Store>();
1446   }
1447 
1448   log_develop_trace(continuations)("finish_freeze: has_mixed_frames: %d", chunk->has_mixed_frames());
1449   if (lt.develop_is_enabled()) {
1450     LogStream ls(lt);
1451     chunk->print_on(true, &ls);
1452   }
1453 
1454   if (lt.develop_is_enabled()) {
1455     LogStream ls(lt);
1456     ls.print_cr("top hframe after (freeze):");
1457     assert(_cont.last_frame().is_heap_frame(), "should be");
1458     _cont.last_frame().print_on(&ls);
1459     DEBUG_ONLY(print_frame_layout(top, false, &ls);)
1460   }
1461 
1462   assert(_cont.chunk_invariant(), "");
1463 }
1464 
1465 inline bool FreezeBase::stack_overflow() { // detect stack overflow in recursive native code
1466   JavaThread* t = !_preempt ? _thread : JavaThread::current();
1467   assert(t == JavaThread::current(), "");
1468   if (os::current_stack_pointer() < t->stack_overflow_state()->shadow_zone_safe_limit()) {
1469     if (!_preempt) {
1470       ContinuationWrapper::SafepointOp so(t, _cont); // could also call _cont.done() instead
1471       Exceptions::_throw_msg(t, __FILE__, __LINE__, vmSymbols::java_lang_StackOverflowError(), "Stack overflow while freezing");
1472     }
1473     return true;
1474   }
1475   return false;
1476 }
1477 
1478 class StackChunkAllocator : public MemAllocator {
1479   const size_t                                 _stack_size;
1480   int                                          _argsize_md;
1481   ContinuationWrapper&                         _continuation_wrapper;
1482   JvmtiSampledObjectAllocEventCollector* const _jvmti_event_collector;
1483   mutable bool                                 _took_slow_path;
1484 
1485   // Does the minimal amount of initialization needed for a TLAB allocation.
1486   // We don't need to do a full initialization, as such an allocation need not be immediately walkable.
1487   virtual oop initialize(HeapWord* mem) const override {
1488     assert(_stack_size > 0, "");
1489     assert(_stack_size <= max_jint, "");
1490     assert(_word_size > _stack_size, "");
1491 
1492     // zero out fields (but not the stack)
1493     const size_t hs = oopDesc::header_size();
1494     if (oopDesc::has_klass_gap()) {
1495       oopDesc::set_klass_gap(mem, 0);
1496     }
1497     Copy::fill_to_aligned_words(mem + hs, vmClasses::StackChunk_klass()->size_helper() - hs);
1498 
1499     int bottom = (int)_stack_size - _argsize_md;
1500 
1501     jdk_internal_vm_StackChunk::set_size(mem, (int)_stack_size);
1502     jdk_internal_vm_StackChunk::set_bottom(mem, bottom);
1503     jdk_internal_vm_StackChunk::set_sp(mem, bottom);
1504 
1505     return finish(mem);
1506   }
1507 
1508   stackChunkOop allocate_fast() const {
1509     if (!UseTLAB) {
1510       return nullptr;
1511     }
1512 
1513     HeapWord* const mem = MemAllocator::mem_allocate_inside_tlab_fast();
1514     if (mem == nullptr) {
1515       return nullptr;
1516     }
1517 
1518     oop obj = initialize(mem);
1519     return stackChunkOopDesc::cast(obj);
1520   }
1521 
1522 public:
1523   StackChunkAllocator(Klass* klass,
1524                       size_t word_size,
1525                       Thread* thread,
1526                       size_t stack_size,
1527                       int argsize_md,
1528                       ContinuationWrapper& continuation_wrapper,
1529                       JvmtiSampledObjectAllocEventCollector* jvmti_event_collector)
1530     : MemAllocator(klass, word_size, thread),
1531       _stack_size(stack_size),
1532       _argsize_md(argsize_md),
1533       _continuation_wrapper(continuation_wrapper),
1534       _jvmti_event_collector(jvmti_event_collector),
1535       _took_slow_path(false) {}
1536 
1537   // Provides it's own, specialized allocation which skips instrumentation
1538   // if the memory can be allocated without going to a slow-path.
1539   stackChunkOop allocate() const {
1540     // First try to allocate without any slow-paths or instrumentation.
1541     stackChunkOop obj = allocate_fast();
1542     if (obj != nullptr) {
1543       return obj;
1544     }
1545 
1546     // Now try full-blown allocation with all expensive operations,
1547     // including potentially safepoint operations.
1548     _took_slow_path = true;
1549 
1550     // Protect unhandled Loom oops
1551     ContinuationWrapper::SafepointOp so(_thread, _continuation_wrapper);
1552 
1553     // Can safepoint
1554     _jvmti_event_collector->start();
1555 
1556     // Can safepoint
1557     return stackChunkOopDesc::cast(MemAllocator::allocate());
1558   }
1559 
1560   bool took_slow_path() const {
1561     return _took_slow_path;
1562   }
1563 };
1564 
1565 template <typename ConfigT>
1566 stackChunkOop Freeze<ConfigT>::allocate_chunk(size_t stack_size, int argsize_md) {
1567   log_develop_trace(continuations)("allocate_chunk allocating new chunk");
1568 
1569   InstanceStackChunkKlass* klass = InstanceStackChunkKlass::cast(vmClasses::StackChunk_klass());
1570   size_t size_in_words = klass->instance_size(stack_size);
1571 
1572   if (CollectedHeap::stack_chunk_max_size() > 0 && size_in_words >= CollectedHeap::stack_chunk_max_size()) {
1573     if (!_preempt) {
1574       throw_stack_overflow_on_humongous_chunk();
1575     }
1576     return nullptr;
1577   }
1578 
1579   JavaThread* current = _preempt ? JavaThread::current() : _thread;
1580   assert(current == JavaThread::current(), "should be current");
1581 
1582   // Allocate the chunk.
1583   //
1584   // This might safepoint while allocating, but all safepointing due to
1585   // instrumentation have been deferred. This property is important for
1586   // some GCs, as this ensures that the allocated object is in the young
1587   // generation / newly allocated memory.
1588   StackChunkAllocator allocator(klass, size_in_words, current, stack_size, argsize_md, _cont, _jvmti_event_collector);
1589   stackChunkOop chunk = allocator.allocate();
1590 
1591   if (chunk == nullptr) {
1592     return nullptr; // OOME
1593   }
1594 
1595   // assert that chunk is properly initialized
1596   assert(chunk->stack_size() == (int)stack_size, "");
1597   assert(chunk->size() >= stack_size, "chunk->size(): %zu size: %zu", chunk->size(), stack_size);
1598   assert(chunk->sp() == chunk->bottom(), "");
1599   assert((intptr_t)chunk->start_address() % 8 == 0, "");
1600   assert(chunk->max_thawing_size() == 0, "");
1601   assert(chunk->pc() == nullptr, "");
1602   assert(chunk->is_empty(), "");
1603   assert(chunk->flags() == 0, "");
1604   assert(chunk->is_gc_mode() == false, "");
1605   assert(chunk->lockstack_size() == 0, "");
1606 
1607   // fields are uninitialized
1608   chunk->set_parent_access<IS_DEST_UNINITIALIZED>(_cont.last_nonempty_chunk());
1609   chunk->set_cont_access<IS_DEST_UNINITIALIZED>(_cont.continuation());
1610 
1611 #if INCLUDE_ZGC
1612   if (UseZGC) {
1613     ZStackChunkGCData::initialize(chunk);
1614     assert(!chunk->requires_barriers(), "ZGC always allocates in the young generation");
1615     _barriers = false;
1616   } else
1617 #endif
1618 #if INCLUDE_SHENANDOAHGC
1619   if (UseShenandoahGC) {
1620     ShenandoahStackChunkGCData::initialize(chunk);
1621     _barriers = chunk->requires_barriers();
1622   } else
1623 #endif
1624   {
1625     if (!allocator.took_slow_path()) {
1626       // Guaranteed to be in young gen / newly allocated memory
1627       assert(!chunk->requires_barriers(), "Unfamiliar GC requires barriers on TLAB allocation");
1628       _barriers = false;
1629     } else {
1630       // Some GCs could put direct allocations in old gen for slow-path
1631       // allocations; need to explicitly check if that was the case.
1632       _barriers = chunk->requires_barriers();
1633     }
1634   }
1635 
1636   if (_barriers) {
1637     log_develop_trace(continuations)("allocation requires barriers");
1638   }
1639 
1640   assert(chunk->parent() == nullptr || chunk->parent()->is_stackChunk(), "");
1641 
1642   return chunk;
1643 }
1644 
1645 void FreezeBase::throw_stack_overflow_on_humongous_chunk() {
1646   ContinuationWrapper::SafepointOp so(_thread, _cont); // could also call _cont.done() instead
1647   Exceptions::_throw_msg(_thread, __FILE__, __LINE__, vmSymbols::java_lang_StackOverflowError(), "Humongous stack chunk");
1648 }
1649 
1650 class AnchorMark : public StackObj {
1651   JavaThread* _current;
1652   frame& _top_frame;
1653   intptr_t* _last_sp_from_frame;
1654   bool _is_interpreted;
1655 
1656  public:
1657   AnchorMark(JavaThread* current, frame& f) : _current(current), _top_frame(f), _is_interpreted(false) {
1658     intptr_t* sp = anchor_mark_set_pd();
1659     set_anchor(_current, sp);
1660   }
1661   ~AnchorMark() {
1662     clear_anchor(_current);
1663     anchor_mark_clear_pd();
1664   }
1665   inline intptr_t* anchor_mark_set_pd();
1666   inline void anchor_mark_clear_pd();
1667 };
1668 
1669 #if INCLUDE_JVMTI
1670 static int num_java_frames(ContinuationWrapper& cont) {
1671   ResourceMark rm; // used for scope traversal in num_java_frames(nmethod*, address)
1672   int count = 0;
1673   for (stackChunkOop chunk = cont.tail(); chunk != nullptr; chunk = chunk->parent()) {
1674     count += chunk->num_java_frames();
1675   }
1676   return count;
1677 }
1678 
1679 static void invalidate_jvmti_stack(JavaThread* thread) {
1680   JvmtiThreadState *state = thread->jvmti_thread_state();
1681   if (state != nullptr) {
1682     state->invalidate_cur_stack_depth();
1683   }
1684 }
1685 
1686 static void jvmti_yield_cleanup(JavaThread* thread, ContinuationWrapper& cont) {
1687   if (!cont.entry()->is_virtual_thread()) {
1688     if (JvmtiExport::has_frame_pops(thread)) {
1689       int num_frames = num_java_frames(cont);
1690 
1691       ContinuationWrapper::SafepointOp so(Thread::current(), cont);
1692       JvmtiExport::continuation_yield_cleanup(thread, num_frames);
1693     }
1694     invalidate_jvmti_stack(thread);
1695   }
1696 }
1697 
1698 static void jvmti_mount_end(JavaThread* current, ContinuationWrapper& cont, frame top, Continuation::preempt_kind pk) {
1699   assert(current->vthread() != nullptr, "must be");
1700 
1701   HandleMarkCleaner hm(current);  // Cleanup all handles (including so._conth) before returning to Java.
1702   Handle vth(current, current->vthread());
1703   ContinuationWrapper::SafepointOp so(current, cont);
1704   AnchorMark am(current, top);  // Set anchor so that the stack is walkable.
1705 
1706   JRT_BLOCK
1707     MountUnmountDisabler::end_transition(current, vth(), true /*is_mount*/, false /*is_thread_start*/);
1708 
1709     if (current->pending_contended_entered_event()) {
1710       // No monitor JVMTI events for ObjectLocker case.
1711       if (pk != Continuation::object_locker) {
1712         JvmtiExport::post_monitor_contended_entered(current, current->contended_entered_monitor());
1713       }
1714       current->set_contended_entered_monitor(nullptr);
1715     }
1716   JRT_BLOCK_END
1717 }
1718 #endif // INCLUDE_JVMTI
1719 
1720 #ifdef ASSERT
1721 // There are no interpreted frames if we're not called from the interpreter and we haven't ancountered an i2c
1722 // adapter or called Deoptimization::unpack_frames. As for native frames, upcalls from JNI also go through the
1723 // interpreter (see JavaCalls::call_helper), while the UpcallLinker explicitly sets cont_fastpath.
1724 bool FreezeBase::check_valid_fast_path() {
1725   ContinuationEntry* ce = _thread->last_continuation();
1726   RegisterMap map(_thread,
1727                   RegisterMap::UpdateMap::skip,
1728                   RegisterMap::ProcessFrames::skip,
1729                   RegisterMap::WalkContinuation::skip);
1730   map.set_include_argument_oops(false);
1731   bool is_top_frame = true;
1732   for (frame f = freeze_start_frame(); Continuation::is_frame_in_continuation(ce, f); f = f.sender(&map), is_top_frame = false) {
1733     if (!((f.is_compiled_frame() && !f.is_deoptimized_frame()) || (is_top_frame && (f.is_runtime_frame() || f.is_native_frame())))) {
1734       return false;
1735     }
1736   }
1737   return true;
1738 }
1739 
1740 static void verify_frame_kind(frame& top, Continuation::preempt_kind preempt_kind, Method** m_ptr, const char** code_name_ptr, int* bci_ptr, stackChunkOop chunk) {
1741   Method* m;
1742   const char* code_name;
1743   int bci;
1744   ResourceMark rm;
1745 
1746   if (preempt_kind == Continuation::monitorenter) {
1747     assert(top.is_interpreted_frame() || top.is_runtime_frame(), "unexpected %sframe",
1748       top.is_compiled_frame() ? "compiled " : top.is_native_frame() ? "native " : "");
1749     bool at_sync_method;
1750     if (top.is_interpreted_frame()) {
1751       m = top.interpreter_frame_method();
1752       assert(!m->is_native() || m->is_synchronized(), "invalid method %s", m->external_name());
1753       address bcp = top.interpreter_frame_bcp();
1754       assert(bcp != nullptr || m->is_native(), "");
1755       at_sync_method = m->is_synchronized() && (bcp == nullptr || bcp == m->code_base());
1756       // bcp is advanced on monitorenter before making the VM call, adjust for that.
1757       bool at_sync_bytecode = bcp > m->code_base() && Bytecode(m, bcp - 1).code() == Bytecodes::Code::_monitorenter;
1758       assert(at_sync_method || at_sync_bytecode, "");
1759       bci = at_sync_method ? -1 : top.interpreter_frame_bci();
1760     } else {
1761       JavaThread* current = JavaThread::current();
1762       CodeBlob* cb = top.cb();
1763       RegisterMap reg_map(current,
1764                   RegisterMap::UpdateMap::skip,
1765                   RegisterMap::ProcessFrames::skip,
1766                   RegisterMap::WalkContinuation::include);
1767       if (top.is_heap_frame()) {
1768         assert(chunk != nullptr, "");
1769         reg_map.set_stack_chunk(chunk);
1770         top = chunk->relativize(top);
1771         top.set_frame_index(0);
1772       }
1773       frame fr = top.sender(&reg_map);
1774       vframe*  vf  = vframe::new_vframe(&fr, &reg_map, current);
1775       compiledVFrame* cvf = compiledVFrame::cast(vf);
1776       m = cvf->method();
1777       bci = cvf->scope()->bci();
1778       at_sync_method = bci == SynchronizationEntryBCI;
1779       assert(!at_sync_method || m->is_synchronized(), "bci is %d but method %s is not synchronized", bci, m->external_name());
1780       bool is_c1_monitorenter = false, is_c2_monitorenter = false;
1781       COMPILER1_PRESENT(is_c1_monitorenter = cb == Runtime1::blob_for(StubId::c1_monitorenter_id) ||
1782                                              cb == Runtime1::blob_for(StubId::c1_monitorenter_nofpu_id);)
1783       COMPILER2_PRESENT(is_c2_monitorenter = cb == CodeCache::find_blob(OptoRuntime::complete_monitor_locking_Java());)
1784       assert(is_c1_monitorenter || is_c2_monitorenter, "wrong runtime stub frame");
1785     }
1786     code_name = at_sync_method ? "synchronized method" : "monitorenter";
1787   } else if (preempt_kind == Continuation::object_wait) {
1788     assert(top.is_interpreted_frame() || top.is_native_frame(), "");
1789     m  = top.is_interpreted_frame() ? top.interpreter_frame_method() : top.cb()->as_nmethod()->method();
1790     assert(m->is_object_wait0(), "");
1791     bci = 0;
1792     code_name = "";
1793   } else {
1794     assert(preempt_kind == Continuation::object_locker, "invalid preempt kind");
1795     assert(top.is_interpreted_frame(), "");
1796     m = top.interpreter_frame_method();
1797     Bytecode current_bytecode = Bytecode(m, top.interpreter_frame_bcp());
1798     Bytecodes::Code code = current_bytecode.code();
1799     assert(code == Bytecodes::Code::_new || code == Bytecodes::Code::_invokestatic ||
1800            (code == Bytecodes::Code::_getstatic || code == Bytecodes::Code::_putstatic), "invalid bytecode");
1801     bci = top.interpreter_frame_bci();
1802     code_name = Bytecodes::name(current_bytecode.code());
1803   }
1804   assert(bci >= 0 || m->is_synchronized(), "invalid bci:%d at method %s", bci, m->external_name());
1805 
1806   if (m_ptr != nullptr) {
1807     *m_ptr = m;
1808     *code_name_ptr = code_name;
1809     *bci_ptr = bci;
1810   }
1811 }
1812 
1813 static void log_preempt_after_freeze(const ContinuationWrapper& cont) {
1814   JavaThread* current = cont.thread();
1815   int64_t tid = current->monitor_owner_id();
1816 
1817   StackChunkFrameStream<ChunkFrames::Mixed> sfs(cont.tail());
1818   frame top_frame = sfs.to_frame();
1819   bool at_init = current->at_preemptable_init();
1820   bool at_enter = current->current_pending_monitor() != nullptr;
1821   bool at_wait = current->current_waiting_monitor() != nullptr;
1822   assert((at_enter && !at_wait) || (!at_enter && at_wait), "");
1823   Continuation::preempt_kind pk = at_init ? Continuation::object_locker : at_enter ? Continuation::monitorenter : Continuation::object_wait;
1824 
1825   Method* m = nullptr;
1826   const char* code_name = nullptr;
1827   int bci = InvalidFrameStateBci;
1828   verify_frame_kind(top_frame, pk, &m, &code_name, &bci, cont.tail());
1829   assert(m != nullptr && code_name != nullptr && bci != InvalidFrameStateBci, "should be set");
1830 
1831   ResourceMark rm(current);
1832   if (bci < 0) {
1833     log_trace(continuations, preempt)("Preempted " INT64_FORMAT " while synchronizing on %smethod %s", tid, m->is_native() ? "native " : "", m->external_name());
1834   } else if (m->is_object_wait0()) {
1835     log_trace(continuations, preempt)("Preempted " INT64_FORMAT " at native method %s", tid, m->external_name());
1836   } else {
1837     Klass* k = current->preempt_init_klass();
1838     assert(k != nullptr || !at_init, "");
1839     log_trace(continuations, preempt)("Preempted " INT64_FORMAT " at %s(bci:%d) in method %s %s%s", tid, code_name, bci,
1840             m->external_name(), at_init ? "trying to initialize klass " : "", at_init ? k->external_name() : "");
1841   }
1842 }
1843 #endif // ASSERT
1844 
1845 static inline freeze_result freeze_epilog(ContinuationWrapper& cont) {
1846   verify_continuation(cont.continuation());
1847   assert(!cont.is_empty(), "");
1848 
1849   log_develop_debug(continuations)("=== End of freeze cont ### #" INTPTR_FORMAT, cont.hash());
1850   return freeze_ok;
1851 }
1852 
1853 static freeze_result freeze_epilog(JavaThread* thread, ContinuationWrapper& cont, freeze_result res) {
1854   if (UNLIKELY(res != freeze_ok)) {
1855     JFR_ONLY(thread->set_last_freeze_fail_result(res);)
1856     verify_continuation(cont.continuation());
1857     log_develop_trace(continuations)("=== end of freeze (fail %d)", res);
1858     return res;
1859   }
1860 
1861   JVMTI_ONLY(jvmti_yield_cleanup(thread, cont)); // can safepoint
1862   return freeze_epilog(cont);
1863 }
1864 
1865 static freeze_result preempt_epilog(ContinuationWrapper& cont, freeze_result res, frame& old_last_frame) {
1866   if (UNLIKELY(res != freeze_ok)) {
1867     verify_continuation(cont.continuation());
1868     log_develop_trace(continuations)("=== end of freeze (fail %d)", res);
1869     return res;
1870   }
1871 
1872   // Set up things so that on return to Java we jump to preempt stub.
1873   patch_return_pc_with_preempt_stub(old_last_frame);
1874   cont.tail()->set_preempted(true);
1875   DEBUG_ONLY(log_preempt_after_freeze(cont);)
1876   return freeze_epilog(cont);
1877 }
1878 
1879 template<typename ConfigT, bool preempt>
1880 static inline freeze_result freeze_internal(JavaThread* current, intptr_t* const sp) {
1881   assert(!current->has_pending_exception(), "");
1882 
1883 #ifdef ASSERT
1884   log_trace(continuations)("~~~~ freeze sp: " INTPTR_FORMAT "JavaThread: " INTPTR_FORMAT, p2i(current->last_continuation()->entry_sp()), p2i(current));
1885   log_frames(current);
1886 #endif
1887 
1888   CONT_JFR_ONLY(EventContinuationFreeze event;)
1889 
1890   ContinuationEntry* entry = current->last_continuation();
1891 
1892   oop oopCont = entry->cont_oop(current);
1893   assert(oopCont == current->last_continuation()->cont_oop(current), "");
1894   assert(ContinuationEntry::assert_entry_frame_laid_out(current), "");
1895 
1896   verify_continuation(oopCont);
1897   ContinuationWrapper cont(current, oopCont);
1898   log_develop_debug(continuations)("FREEZE #" INTPTR_FORMAT " " INTPTR_FORMAT, cont.hash(), p2i((oopDesc*)oopCont));
1899 
1900   assert(entry->is_virtual_thread() == (entry->scope(current) == java_lang_VirtualThread::vthread_scope()), "");
1901 
1902   if (entry->is_pinned()) {
1903     log_develop_debug(continuations)("PINNED due to critical section");
1904     verify_continuation(cont.continuation());
1905     const freeze_result res = freeze_pinned_cs;
1906     if (!preempt) {
1907       JFR_ONLY(current->set_last_freeze_fail_result(res);)
1908     }
1909     log_develop_trace(continuations)("=== end of freeze (fail %d)", res);
1910     // Avoid Thread.yield() loops without safepoint polls.
1911     if (SafepointMechanism::should_process(current) && !preempt) {
1912       cont.done(); // allow safepoint
1913       ThreadInVMfromJava tivmfj(current);
1914     }
1915     return res;
1916   }
1917 
1918   Freeze<ConfigT> freeze(current, cont, sp, preempt);
1919 
1920   assert(!current->cont_fastpath() || freeze.check_valid_fast_path(), "");
1921   bool fast = UseContinuationFastPath && current->cont_fastpath();
1922   if (fast && freeze.size_if_fast_freeze_available() > 0) {
1923     freeze.freeze_fast_existing_chunk();
1924     CONT_JFR_ONLY(freeze.jfr_info().post_jfr_event(&event, oopCont, current);)
1925     return !preempt ? freeze_epilog(cont) : preempt_epilog(cont, freeze_ok, freeze.last_frame());
1926   }
1927 
1928   if (preempt) {
1929     JvmtiSampledObjectAllocEventCollector jsoaec(false);
1930     freeze.set_jvmti_event_collector(&jsoaec);
1931 
1932     freeze_result res = fast ? freeze.try_freeze_fast() : freeze.freeze_slow();
1933 
1934     CONT_JFR_ONLY(freeze.jfr_info().post_jfr_event(&event, oopCont, current);)
1935     preempt_epilog(cont, res, freeze.last_frame());
1936     return res;
1937   }
1938 
1939   log_develop_trace(continuations)("chunk unavailable; transitioning to VM");
1940   assert(current == JavaThread::current(), "must be current thread");
1941   JRT_BLOCK
1942     // delays a possible JvmtiSampledObjectAllocEventCollector in alloc_chunk
1943     JvmtiSampledObjectAllocEventCollector jsoaec(false);
1944     freeze.set_jvmti_event_collector(&jsoaec);
1945 
1946     freeze_result res = fast ? freeze.try_freeze_fast() : freeze.freeze_slow();
1947 
1948     CONT_JFR_ONLY(freeze.jfr_info().post_jfr_event(&event, oopCont, current);)
1949     freeze_epilog(current, cont, res);
1950     cont.done(); // allow safepoint in the transition back to Java
1951     return res;
1952   JRT_BLOCK_END
1953 }
1954 
1955 static freeze_result is_pinned0(JavaThread* thread, oop cont_scope, bool safepoint) {
1956   ContinuationEntry* entry = thread->last_continuation();
1957   if (entry == nullptr) {
1958     return freeze_ok;
1959   }
1960   if (entry->is_pinned()) {
1961     return freeze_pinned_cs;
1962   }
1963 
1964   RegisterMap map(thread,
1965                   RegisterMap::UpdateMap::include,
1966                   RegisterMap::ProcessFrames::skip,
1967                   RegisterMap::WalkContinuation::skip);
1968   map.set_include_argument_oops(false);
1969   frame f = thread->last_frame();
1970 
1971   if (!safepoint) {
1972     f = f.sender(&map); // this is the yield frame
1973   } else { // safepoint yield
1974 #if (defined(X86) || defined(AARCH64) || defined(RISCV64)) && !defined(ZERO)
1975     f.set_fp(f.real_fp()); // Instead of this, maybe in ContinuationWrapper::set_last_frame always use the real_fp?
1976 #else
1977     Unimplemented();
1978 #endif
1979     if (!Interpreter::contains(f.pc())) {
1980       assert(ContinuationHelper::Frame::is_stub(f.cb()), "must be");
1981       assert(f.oop_map() != nullptr, "must be");
1982       f.oop_map()->update_register_map(&f, &map); // we have callee-save registers in this case
1983     }
1984   }
1985 
1986   while (true) {
1987     if ((f.is_interpreted_frame() && f.interpreter_frame_method()->is_native()) || f.is_native_frame()) {
1988       return freeze_pinned_native;
1989     }
1990 
1991     f = f.sender(&map);
1992     if (!Continuation::is_frame_in_continuation(entry, f)) {
1993       oop scope = jdk_internal_vm_Continuation::scope(entry->cont_oop(thread));
1994       if (scope == cont_scope) {
1995         break;
1996       }
1997       entry = entry->parent();
1998       if (entry == nullptr) {
1999         break;
2000       }
2001       if (entry->is_pinned()) {
2002         return freeze_pinned_cs;
2003       }
2004     }
2005   }
2006   return freeze_ok;
2007 }
2008 
2009 /////////////// THAW ////
2010 
2011 static int thaw_size(stackChunkOop chunk) {
2012   int size = chunk->max_thawing_size();
2013   size += frame::metadata_words; // For the top pc+fp in push_return_frame or top = stack_sp - frame::metadata_words in thaw_fast
2014   size += 2*frame::align_wiggle; // in case of alignments at the top and bottom
2015   return size;
2016 }
2017 
2018 // make room on the stack for thaw
2019 // returns the size in bytes, or 0 on failure
2020 static inline int prepare_thaw_internal(JavaThread* thread, bool return_barrier) {
2021   log_develop_trace(continuations)("~~~~ prepare_thaw return_barrier: %d", return_barrier);
2022 
2023   assert(thread == JavaThread::current(), "");
2024 
2025   ContinuationEntry* ce = thread->last_continuation();
2026   assert(ce != nullptr, "");
2027   oop continuation = ce->cont_oop(thread);
2028   assert(continuation == get_continuation(thread), "");
2029   verify_continuation(continuation);
2030 
2031   stackChunkOop chunk = jdk_internal_vm_Continuation::tail(continuation);
2032   assert(chunk != nullptr, "");
2033 
2034   // The tail can be empty because it might still be available for another freeze.
2035   // However, here we want to thaw, so we get rid of it (it will be GCed).
2036   if (UNLIKELY(chunk->is_empty())) {
2037     chunk = chunk->parent();
2038     assert(chunk != nullptr, "");
2039     assert(!chunk->is_empty(), "");
2040     jdk_internal_vm_Continuation::set_tail(continuation, chunk);
2041   }
2042 
2043   // Verification
2044   chunk->verify();
2045   assert(chunk->max_thawing_size() > 0, "chunk invariant violated; expected to not be empty");
2046 
2047   // Only make space for the last chunk because we only thaw from the last chunk
2048   int size = thaw_size(chunk) << LogBytesPerWord;
2049 
2050   const address bottom = (address)thread->last_continuation()->entry_sp();
2051   // 300 is an estimate for stack size taken for this native code, in addition to StackShadowPages
2052   // for the Java frames in the check below.
2053   if (!stack_overflow_check(thread, size + 300, bottom)) {
2054     return 0;
2055   }
2056 
2057   log_develop_trace(continuations)("prepare_thaw bottom: " INTPTR_FORMAT " top: " INTPTR_FORMAT " size: %d",
2058                               p2i(bottom), p2i(bottom - size), size);
2059   return size;
2060 }
2061 
2062 class ThawBase : public StackObj {
2063 protected:
2064   JavaThread* _thread;
2065   ContinuationWrapper& _cont;
2066   CONT_JFR_ONLY(FreezeThawJfrInfo _jfr_info;)
2067 
2068   intptr_t* _fastpath;
2069   bool _barriers;
2070   bool _preempted_case;
2071   bool _should_patch_caller_pc;
2072   bool _process_args_at_top;
2073   intptr_t* _top_unextended_sp_before_thaw;
2074   int _align_size;
2075   DEBUG_ONLY(intptr_t* _top_stack_address;)
2076   DEBUG_ONLY(address _caller_raw_pc;)
2077 
2078   // Only used for preemption on ObjectLocker
2079   ObjectMonitor* _init_lock;
2080 
2081   StackChunkFrameStream<ChunkFrames::Mixed> _stream;
2082 
2083   NOT_PRODUCT(int _frames;)
2084 
2085 protected:
2086   ThawBase(JavaThread* thread, ContinuationWrapper& cont) :
2087       _thread(thread), _cont(cont),
2088       _fastpath(nullptr) {
2089     DEBUG_ONLY(_top_unextended_sp_before_thaw = nullptr;)
2090     assert (cont.tail() != nullptr, "no last chunk");
2091     DEBUG_ONLY(_top_stack_address = _cont.entrySP() - thaw_size(cont.tail());)
2092   }
2093 
2094   void clear_chunk(stackChunkOop chunk);
2095   template<bool check_stub>
2096   int remove_top_compiled_frame_from_chunk(stackChunkOop chunk, int &argsize);
2097   int remove_scalarized_frames(StackChunkFrameStream<ChunkFrames::CompiledOnly>& scfs, int &argsize);
2098   void check_top_for_deoptimization(stackChunkOop chunk);
2099   void copy_from_chunk(intptr_t* from, intptr_t* to, int size);
2100 
2101   void thaw_lockstack(stackChunkOop chunk);
2102 
2103   // fast path
2104   inline void prefetch_chunk_pd(void* start, int size_words);
2105   void patch_return(intptr_t* sp, bool is_last);
2106 
2107   intptr_t* handle_preempted_continuation(intptr_t* sp, Continuation::preempt_kind preempt_kind, bool fast_case);
2108   inline intptr_t* push_cleanup_continuation();
2109   inline intptr_t* push_preempt_adapter();
2110   intptr_t* redo_vmcall(JavaThread* current, frame& top);
2111   void throw_interrupted_exception(JavaThread* current, frame& top);
2112 
2113   void recurse_thaw(const frame& heap_frame, frame& caller, int num_frames, bool top_on_preempt_case);
2114   void finish_thaw(frame& f);
2115 
2116 private:
2117   template<typename FKind> bool recurse_thaw_java_frame(frame& caller, int num_frames);
2118   void finalize_thaw(frame& entry, int argsize);
2119 
2120   inline bool seen_by_gc();
2121 
2122   inline void before_thaw_java_frame(const frame& hf, const frame& caller, bool bottom, int num_frame);
2123   inline void after_thaw_java_frame(const frame& f, bool bottom);
2124   inline void patch(frame& f, const frame& caller, bool bottom);
2125   void clear_bitmap_bits(address start, address end);
2126 
2127   NOINLINE void recurse_thaw_interpreted_frame(const frame& hf, frame& caller, int num_frames, bool is_top);
2128   void recurse_thaw_compiled_frame(const frame& hf, frame& caller, int num_frames, bool stub_caller);
2129   void recurse_thaw_stub_frame(const frame& hf, frame& caller, int num_frames);
2130   void recurse_thaw_native_frame(const frame& hf, frame& caller, int num_frames);
2131 
2132   void push_return_frame(const frame& f);
2133   inline frame new_entry_frame();
2134   template<typename FKind> frame new_stack_frame(const frame& hf, frame& caller, bool bottom, int size_adjust = 0);
2135   inline void patch_pd(frame& f, const frame& sender);
2136   inline void patch_pd(frame& f, intptr_t* caller_sp);
2137   inline intptr_t* align(const frame& hf, intptr_t* frame_sp, frame& caller, bool bottom);
2138 
2139   void maybe_set_fastpath(intptr_t* sp) { if (sp > _fastpath) _fastpath = sp; }
2140 
2141   static inline void derelativize_interpreted_frame_metadata(const frame& hf, const frame& f);
2142 
2143  public:
2144   CONT_JFR_ONLY(FreezeThawJfrInfo& jfr_info() { return _jfr_info; })
2145 };
2146 
2147 template <typename ConfigT>
2148 class Thaw : public ThawBase {
2149 public:
2150   Thaw(JavaThread* thread, ContinuationWrapper& cont) : ThawBase(thread, cont) {}
2151 
2152   inline bool can_thaw_fast(stackChunkOop chunk) {
2153     return    !_barriers
2154            &&  _thread->cont_fastpath_thread_state()
2155            && !chunk->has_thaw_slowpath_condition()
2156            && !PreserveFramePointer;
2157   }
2158 
2159   inline intptr_t* thaw(Continuation::thaw_kind kind);
2160   template<bool check_stub = false>
2161   NOINLINE intptr_t* thaw_fast(stackChunkOop chunk);
2162   NOINLINE intptr_t* thaw_slow(stackChunkOop chunk, Continuation::thaw_kind kind);
2163   inline void patch_caller_links(intptr_t* sp, intptr_t* bottom);
2164 };
2165 
2166 template <typename ConfigT>
2167 inline intptr_t* Thaw<ConfigT>::thaw(Continuation::thaw_kind kind) {
2168   verify_continuation(_cont.continuation());
2169   assert(!jdk_internal_vm_Continuation::done(_cont.continuation()), "");
2170   assert(!_cont.is_empty(), "");
2171 
2172   stackChunkOop chunk = _cont.tail();
2173   assert(chunk != nullptr, "guaranteed by prepare_thaw");
2174   assert(!chunk->is_empty(), "guaranteed by prepare_thaw");
2175 
2176   _barriers = chunk->requires_barriers();
2177   return (LIKELY(can_thaw_fast(chunk))) ? thaw_fast(chunk)
2178                                         : thaw_slow(chunk, kind);
2179 }
2180 
2181 class ReconstructedStack : public StackObj {
2182   intptr_t* _base;  // _cont.entrySP(); // top of the entry frame
2183   int _thaw_size;
2184   int _argsize;
2185 public:
2186   ReconstructedStack(intptr_t* base, int thaw_size, int argsize)
2187   : _base(base), _thaw_size(thaw_size - (argsize == 0 ? frame::metadata_words_at_top : 0)), _argsize(argsize) {
2188     // The only possible source of misalignment is stack-passed arguments b/c compiled frames are 16-byte aligned.
2189     assert(argsize != 0 || (_base - _thaw_size) == ContinuationHelper::frame_align_pointer(_base - _thaw_size), "");
2190     // We're at most one alignment word away from entrySP
2191     assert(_base - 1 <= top() + total_size() + frame::metadata_words_at_bottom, "missed entry frame");
2192   }
2193 
2194   int entry_frame_extension() const { return _argsize + (_argsize > 0 ? frame::metadata_words_at_top : 0); }
2195 
2196   // top and bottom stack pointers
2197   intptr_t* sp() const { return ContinuationHelper::frame_align_pointer(_base - _thaw_size); }
2198   intptr_t* bottom_sp() const { return ContinuationHelper::frame_align_pointer(_base - entry_frame_extension()); }
2199 
2200   // several operations operate on the totality of the stack being reconstructed,
2201   // including the metadata words
2202   intptr_t* top() const { return sp() - frame::metadata_words_at_bottom;  }
2203   int total_size() const { return _thaw_size + frame::metadata_words_at_bottom; }
2204 };
2205 
2206 inline void ThawBase::clear_chunk(stackChunkOop chunk) {
2207   chunk->set_sp(chunk->bottom());
2208   chunk->set_max_thawing_size(0);
2209 }
2210 
2211 void ThawBase::check_top_for_deoptimization(stackChunkOop chunk) {
2212   StackChunkFrameStream<ChunkFrames::CompiledOnly> f(chunk);
2213   if (f.is_stub()) {
2214     f.next(SmallRegisterMap::instance_no_args(), true /* stop */);
2215     assert(!f.is_done(), "");
2216 
2217     f.get_cb();
2218     assert(f.is_compiled(), "");
2219     if (f.cb()->as_nmethod()->is_marked_for_deoptimization()) {
2220       // The caller of the runtime stub when the continuation is preempted is not at a
2221       // Java call instruction, and so cannot rely on nmethod patching for deopt.
2222       log_develop_trace(continuations)("Deoptimizing runtime stub caller");
2223       f.to_frame().deoptimize(nullptr); // the null thread simply avoids the assertion in deoptimize which we're not set up for
2224     }
2225   }
2226 }
2227 
2228 int ThawBase::remove_scalarized_frames(StackChunkFrameStream<ChunkFrames::CompiledOnly>& f, int &argsize) {
2229   intptr_t* top = f.sp();
2230 
2231   while (f.cb()->as_nmethod()->needs_stack_repair()) {
2232     f.next(SmallRegisterMap::instance_no_args(), false /* stop */);
2233   }
2234   assert(!f.is_done(), "");
2235   assert(f.is_compiled(), "");
2236 
2237   intptr_t* bottom = f.sp() + f.cb()->frame_size();
2238   argsize = f.stack_argsize();
2239   return bottom - top;
2240 }
2241 
2242 template<bool check_stub>
2243 int ThawBase::remove_top_compiled_frame_from_chunk(stackChunkOop chunk, int &argsize) {
2244   bool empty = false;
2245   StackChunkFrameStream<ChunkFrames::CompiledOnly> f(chunk);
2246   DEBUG_ONLY(intptr_t* const chunk_sp = chunk->start_address() + chunk->sp();)
2247   assert(chunk_sp == f.sp(), "");
2248   assert(chunk_sp == f.unextended_sp(), "");
2249 
2250   int frame_size = f.cb()->frame_size();
2251   argsize = f.stack_argsize();
2252 
2253   assert(!f.is_stub() || check_stub, "");
2254   if (check_stub && f.is_stub()) {
2255     // If we don't thaw the top compiled frame too, after restoring the saved
2256     // registers back in Java, we would hit the return barrier to thaw one more
2257     // frame effectively overwriting the restored registers during that call.
2258     f.next(SmallRegisterMap::instance_no_args(), true /* stop */);
2259     assert(!f.is_done(), "");
2260 
2261     f.get_cb();
2262     assert(f.is_compiled(), "");
2263 
2264     if (f.cb()->as_nmethod()->is_marked_for_deoptimization()) {
2265       // The caller of the runtime stub when the continuation is preempted is not at a
2266       // Java call instruction, and so cannot rely on nmethod patching for deopt.
2267       log_develop_trace(continuations)("Deoptimizing runtime stub caller");
2268       f.to_frame().deoptimize(nullptr); // the null thread simply avoids the assertion in deoptimize which we're not set up for
2269     }
2270 
2271     if (f.cb()->as_nmethod()->needs_stack_repair()) {
2272       frame_size += remove_scalarized_frames(f, argsize);
2273     } else {
2274       frame_size += f.cb()->frame_size();
2275       argsize = f.stack_argsize();
2276     }
2277   } else if (f.cb()->as_nmethod()->needs_stack_repair()) {
2278     frame_size = remove_scalarized_frames(f, argsize);
2279   }
2280 
2281   f.next(SmallRegisterMap::instance_no_args(), true /* stop */);
2282   empty = f.is_done();
2283   assert(!empty || argsize == chunk->argsize(), "");
2284 
2285   if (empty) {
2286     clear_chunk(chunk);
2287   } else {
2288     chunk->set_sp(chunk->sp() + frame_size);
2289     chunk->set_max_thawing_size(chunk->max_thawing_size() - frame_size);
2290     // We set chunk->pc to the return pc into the next frame
2291     chunk->set_pc(f.pc());
2292 #ifdef ASSERT
2293     {
2294       intptr_t* retaddr_slot = (chunk_sp
2295                                 + frame_size
2296                                 - frame::sender_sp_ret_address_offset());
2297       assert(f.pc() == ContinuationHelper::return_address_at(retaddr_slot),
2298              "unexpected pc");
2299     }
2300 #endif
2301   }
2302   assert(empty == chunk->is_empty(), "");
2303   // returns the size required to store the frame on stack, and because it is a
2304   // compiled frame, it must include a copy of the arguments passed by the caller
2305   return frame_size + argsize + frame::metadata_words_at_top;
2306 }
2307 
2308 void ThawBase::thaw_lockstack(stackChunkOop chunk) {
2309   int lockStackSize = chunk->lockstack_size();
2310   assert(lockStackSize > 0 && lockStackSize <= LockStack::CAPACITY, "");
2311 
2312   oop tmp_lockstack[LockStack::CAPACITY];
2313   chunk->transfer_lockstack(tmp_lockstack, _barriers);
2314   _thread->lock_stack().move_from_address(tmp_lockstack, lockStackSize);
2315 
2316   chunk->set_lockstack_size(0);
2317   chunk->set_has_lockstack(false);
2318 }
2319 
2320 void ThawBase::copy_from_chunk(intptr_t* from, intptr_t* to, int size) {
2321   assert(to >= _top_stack_address, "overwrote past thawing space"
2322     " to: " INTPTR_FORMAT " top_address: " INTPTR_FORMAT, p2i(to), p2i(_top_stack_address));
2323   assert(to + size <= _cont.entrySP(), "overwrote past thawing space");
2324   _cont.tail()->copy_from_chunk_to_stack(from, to, size);
2325   CONT_JFR_ONLY(_jfr_info.record_size_copied(size);)
2326 }
2327 
2328 void ThawBase::patch_return(intptr_t* sp, bool is_last) {
2329   log_develop_trace(continuations)("thaw_fast patching -- sp: " INTPTR_FORMAT, p2i(sp));
2330 
2331   address pc = !is_last ? StubRoutines::cont_returnBarrier() : _cont.entryPC();
2332   ContinuationHelper::patch_return_address_at(
2333     sp - frame::sender_sp_ret_address_offset(),
2334     pc);
2335 }
2336 
2337 template <typename ConfigT>
2338 template<bool check_stub>
2339 NOINLINE intptr_t* Thaw<ConfigT>::thaw_fast(stackChunkOop chunk) {
2340   assert(chunk == _cont.tail(), "");
2341   assert(!chunk->has_mixed_frames(), "");
2342   assert(!chunk->requires_barriers(), "");
2343   assert(!chunk->has_bitmap(), "");
2344   assert(!_thread->is_interp_only_mode(), "");
2345 
2346   LogTarget(Trace, continuations) lt;
2347   if (lt.develop_is_enabled()) {
2348     LogStream ls(lt);
2349     ls.print_cr("thaw_fast");
2350     chunk->print_on(true, &ls);
2351   }
2352 
2353   // Below this heuristic, we thaw the whole chunk, above it we thaw just one frame.
2354   static const int threshold = 500; // words
2355 
2356   const int full_chunk_size = chunk->stack_size() - chunk->sp(); // this initial size could be reduced if it's a partial thaw
2357   int argsize, thaw_size;
2358 
2359   intptr_t* const chunk_sp = chunk->start_address() + chunk->sp();
2360 
2361   bool partial, empty;
2362   if (LIKELY(!ForceSingleFrameThaw && (full_chunk_size < threshold))) {
2363     prefetch_chunk_pd(chunk->start_address(), full_chunk_size); // prefetch anticipating memcpy starting at highest address
2364 
2365     if (check_stub) {
2366       check_top_for_deoptimization(chunk);
2367     }
2368     partial = false;
2369     argsize = chunk->argsize(); // must be called *before* clearing the chunk
2370     clear_chunk(chunk);
2371     thaw_size = full_chunk_size;
2372     empty = true;
2373   } else { // thaw a single frame
2374     partial = true;
2375     thaw_size = remove_top_compiled_frame_from_chunk<check_stub>(chunk, argsize);
2376     empty = chunk->is_empty();
2377   }
2378 
2379   // Are we thawing the last frame(s) in the continuation
2380   const bool is_last = empty && chunk->parent() == nullptr;
2381   assert(!is_last || argsize == 0, "");
2382 
2383   log_develop_trace(continuations)("thaw_fast partial: %d is_last: %d empty: %d size: %d argsize: %d entrySP: " PTR_FORMAT,
2384                               partial, is_last, empty, thaw_size, argsize, p2i(_cont.entrySP()));
2385 
2386   ReconstructedStack rs(_cont.entrySP(), thaw_size, argsize);
2387 
2388   // also copy metadata words at frame bottom
2389   copy_from_chunk(chunk_sp - frame::metadata_words_at_bottom, rs.top(), rs.total_size());
2390 
2391   // update the ContinuationEntry
2392   _cont.set_argsize(argsize);
2393   log_develop_trace(continuations)("setting entry argsize: %d", _cont.argsize());
2394   assert(rs.bottom_sp() == _cont.entry()->bottom_sender_sp(), "");
2395 
2396   // install the return barrier if not last frame, or the entry's pc if last
2397   patch_return(rs.bottom_sp(), is_last);
2398 
2399   // insert the back links from callee to caller frames
2400   patch_caller_links(rs.top(), rs.top() + rs.total_size());
2401 
2402   assert(is_last == _cont.is_empty(), "");
2403   assert(_cont.chunk_invariant(), "");
2404 
2405 #if CONT_JFR
2406   EventContinuationThawFast e;
2407   if (e.should_commit()) {
2408     e.set_id(cast_from_oop<u8>(chunk));
2409     e.set_size(thaw_size << LogBytesPerWord);
2410     e.set_full(!partial);
2411     e.commit();
2412   }
2413 #endif
2414 
2415 #ifdef ASSERT
2416   if (LoomDeoptAfterThaw) {
2417     frame top(rs.sp());
2418     AnchorMark am(_thread, top);
2419     log_frames(_thread);
2420     do_deopt_after_thaw(_thread);
2421   }
2422 #endif
2423 
2424   return rs.sp();
2425 }
2426 
2427 inline bool ThawBase::seen_by_gc() {
2428   return _barriers || _cont.tail()->is_gc_mode();
2429 }
2430 
2431 static inline void relativize_chunk_concurrently(stackChunkOop chunk) {
2432 #if INCLUDE_ZGC || INCLUDE_SHENANDOAHGC
2433   if (UseZGC || UseShenandoahGC) {
2434     chunk->relativize_derived_pointers_concurrently();
2435   }
2436 #endif
2437 }
2438 
2439 template <typename ConfigT>
2440 NOINLINE intptr_t* Thaw<ConfigT>::thaw_slow(stackChunkOop chunk, Continuation::thaw_kind kind) {
2441   Continuation::preempt_kind preempt_kind;
2442   bool retry_fast_path = false;
2443 
2444   _process_args_at_top = false;
2445   _preempted_case = chunk->preempted();
2446   if (_preempted_case) {
2447     ObjectMonitor* mon = nullptr;
2448     ObjectWaiter* waiter = java_lang_VirtualThread::objectWaiter(_thread->vthread());
2449     if (waiter != nullptr) {
2450       // Mounted again after preemption. Resume the pending monitor operation,
2451       // which will be either a monitorenter or Object.wait() call.
2452       mon = waiter->monitor();
2453       preempt_kind = waiter->is_wait() ? Continuation::object_wait : Continuation::monitorenter;
2454 
2455       bool mon_acquired = mon->resume_operation(_thread, waiter, _cont);
2456       assert(!mon_acquired || mon->has_owner(_thread), "invariant");
2457       if (!mon_acquired) {
2458         // Failed to acquire monitor. Return to enterSpecial to unmount again.
2459         log_develop_trace(continuations, preempt)("Failed to acquire monitor, unmounting again");
2460         return push_cleanup_continuation();
2461       }
2462       chunk = _cont.tail();  // reload oop in case of safepoint in resume_operation (if posting JVMTI events).
2463       JVMTI_ONLY(assert(_thread->contended_entered_monitor() == nullptr || _thread->contended_entered_monitor() == mon, ""));
2464     } else {
2465       // Preemption cancelled on moniterenter or ObjectLocker case. We
2466       // actually acquired the monitor after freezing all frames so no
2467       // need to call resume_operation. If this is the ObjectLocker case
2468       // we released the monitor already at ~ObjectLocker, so _init_lock
2469       // will be set to nullptr below since there is no monitor to release.
2470       preempt_kind = Continuation::monitorenter;
2471     }
2472 
2473     // Call this first to avoid racing with GC threads later when modifying the chunk flags.
2474     relativize_chunk_concurrently(chunk);
2475 
2476     if (chunk->at_klass_init()) {
2477       preempt_kind = Continuation::object_locker;
2478       chunk->set_at_klass_init(false);
2479       _process_args_at_top = chunk->has_args_at_top();
2480       if (_process_args_at_top) {
2481         // Only needed for the top frame which will be thawed.
2482         chunk->set_has_args_at_top(false);
2483       }
2484       assert(waiter == nullptr || mon != nullptr, "should have a monitor");
2485       _init_lock = mon;  // remember monitor since we will need it on handle_preempted_continuation()
2486     }
2487     chunk->set_preempted(false);
2488     retry_fast_path = true;
2489   } else {
2490     relativize_chunk_concurrently(chunk);
2491   }
2492 
2493   // On first thaw after freeze restore oops to the lockstack if any.
2494   assert(chunk->lockstack_size() == 0 || kind == Continuation::thaw_top, "");
2495   if (kind == Continuation::thaw_top && chunk->lockstack_size() > 0) {
2496     thaw_lockstack(chunk);
2497     retry_fast_path = true;
2498   }
2499 
2500   // Retry the fast path now that we possibly cleared the FLAG_HAS_LOCKSTACK
2501   // and FLAG_PREEMPTED flags from the stackChunk.
2502   if (retry_fast_path && can_thaw_fast(chunk)) {
2503     intptr_t* sp = thaw_fast<true>(chunk);
2504     if (_preempted_case) {
2505       return handle_preempted_continuation(sp, preempt_kind, true /* fast_case */);
2506     }
2507     return sp;
2508   }
2509 
2510   LogTarget(Trace, continuations) lt;
2511   if (lt.develop_is_enabled()) {
2512     LogStream ls(lt);
2513     ls.print_cr("thaw slow return_barrier: %d " INTPTR_FORMAT, kind, p2i(chunk));
2514     chunk->print_on(true, &ls);
2515   }
2516 
2517 #if CONT_JFR
2518   EventContinuationThawSlow e;
2519   if (e.should_commit()) {
2520     e.set_id(cast_from_oop<u8>(_cont.continuation()));
2521     e.commit();
2522   }
2523 #endif
2524 
2525   DEBUG_ONLY(_frames = 0;)
2526   _align_size = 0;
2527   int num_frames = kind == Continuation::thaw_top ? 2 : 1;
2528 
2529   _stream = StackChunkFrameStream<ChunkFrames::Mixed>(chunk);
2530   _top_unextended_sp_before_thaw = _stream.unextended_sp();
2531 
2532   frame heap_frame = _stream.to_frame();
2533   if (lt.develop_is_enabled()) {
2534     LogStream ls(lt);
2535     ls.print_cr("top hframe before (thaw):");
2536     assert(heap_frame.is_heap_frame(), "should have created a relative frame");
2537     heap_frame.print_value_on(&ls);
2538   }
2539 
2540   frame caller; // the thawed caller on the stack
2541   _should_patch_caller_pc = false;
2542   recurse_thaw(heap_frame, caller, num_frames, _preempted_case);
2543   finish_thaw(caller); // caller is now the topmost thawed frame
2544   _cont.write();
2545 
2546   assert(_cont.chunk_invariant(), "");
2547 
2548   JVMTI_ONLY(if (!_cont.entry()->is_virtual_thread()) invalidate_jvmti_stack(_thread));
2549 
2550   _thread->set_cont_fastpath(_fastpath);
2551 
2552   intptr_t* sp = caller.sp();
2553 
2554   if (_preempted_case) {
2555     return handle_preempted_continuation(sp, preempt_kind, false /* fast_case */);
2556   }
2557   return sp;
2558 }
2559 
2560 void ThawBase::recurse_thaw(const frame& heap_frame, frame& caller, int num_frames, bool top_on_preempt_case) {
2561   log_develop_debug(continuations)("thaw num_frames: %d", num_frames);
2562   assert(!_cont.is_empty(), "no more frames");
2563   assert(num_frames > 0, "");
2564   assert(!heap_frame.is_empty(), "");
2565 
2566   if (top_on_preempt_case && (heap_frame.is_native_frame() || heap_frame.is_runtime_frame())) {
2567     heap_frame.is_native_frame() ? recurse_thaw_native_frame(heap_frame, caller, 2) : recurse_thaw_stub_frame(heap_frame, caller, 2);
2568   } else if (!heap_frame.is_interpreted_frame()) {
2569     recurse_thaw_compiled_frame(heap_frame, caller, num_frames, false);
2570   } else {
2571     recurse_thaw_interpreted_frame(heap_frame, caller, num_frames, top_on_preempt_case);
2572   }
2573 }
2574 
2575 template<typename FKind>
2576 bool ThawBase::recurse_thaw_java_frame(frame& caller, int num_frames) {
2577   assert(num_frames > 0, "");
2578 
2579   DEBUG_ONLY(_frames++;)
2580 
2581   int argsize = _stream.stack_argsize();
2582   CodeBlob* cb = _stream.cb();
2583 
2584   _stream.next(SmallRegisterMap::instance_no_args());
2585   assert(_stream.to_frame().is_empty() == _stream.is_done(), "");
2586 
2587   // We never leave a compiled caller of an interpreted frame as the top frame in the chunk
2588   // as it makes detecting that situation and adjusting unextended_sp tricky. We also always
2589   // thaw the caller of a frame that needs_stack_repair, as it would otherwise complicate things:
2590   // - Regardless of whether the frame was extended or not, we would need to copy the right arg
2591   //   size if its greater than the one given by the normal method signature (non-scalarized).
2592   // - If the frame was indeed extended, leaving its caller as the top frame would complicate walking
2593   //   the chunk (we need unextended_sp, but we only have sp).
2594   if (num_frames == 1 && !_stream.is_done() && ((FKind::interpreted && _stream.is_compiled()) || (FKind::compiled && cb->as_nmethod_or_null()->needs_stack_repair()))) {
2595     log_develop_trace(continuations)("thawing extra compiled frame to not leave a compiled interpreted-caller at top");
2596     num_frames++;
2597   }
2598 
2599   if (num_frames == 1 || _stream.is_done()) { // end recursion
2600     finalize_thaw(caller, FKind::interpreted ? 0 : argsize);
2601     return true; // bottom
2602   } else { // recurse
2603     recurse_thaw(_stream.to_frame(), caller, num_frames - 1, false /* top_on_preempt_case */);
2604     return false;
2605   }
2606 }
2607 
2608 void ThawBase::finalize_thaw(frame& entry, int argsize) {
2609   stackChunkOop chunk = _cont.tail();
2610 
2611   if (!_stream.is_done()) {
2612     assert(_stream.sp() >= chunk->sp_address(), "");
2613     chunk->set_sp(chunk->to_offset(_stream.sp()));
2614     chunk->set_pc(_stream.pc());
2615   } else {
2616     chunk->set_sp(chunk->bottom());
2617     chunk->set_pc(nullptr);
2618   }
2619   assert(_stream.is_done() == chunk->is_empty(), "");
2620 
2621   int total_thawed = pointer_delta_as_int(_stream.unextended_sp(), _top_unextended_sp_before_thaw);
2622   chunk->set_max_thawing_size(chunk->max_thawing_size() - total_thawed);
2623 
2624   _cont.set_argsize(argsize);
2625   entry = new_entry_frame();
2626 
2627   assert(entry.sp() == _cont.entrySP(), "");
2628   assert(Continuation::is_continuation_enterSpecial(entry), "");
2629   assert(_cont.is_entry_frame(entry), "");
2630   assert(entry.pc() == entry.raw_pc(), "");
2631   DEBUG_ONLY(_caller_raw_pc = entry.pc();)
2632 }
2633 
2634 inline void ThawBase::before_thaw_java_frame(const frame& hf, const frame& caller, bool bottom, int num_frame) {
2635   LogTarget(Trace, continuations) lt;
2636   if (lt.develop_is_enabled()) {
2637     LogStream ls(lt);
2638     ls.print_cr("======== THAWING FRAME: %d", num_frame);
2639     assert(hf.is_heap_frame(), "should be");
2640     hf.print_value_on(&ls);
2641   }
2642   assert(bottom == _cont.is_entry_frame(caller), "bottom: %d is_entry_frame: %d", bottom, _cont.is_entry_frame(hf));
2643 }
2644 
2645 inline void ThawBase::after_thaw_java_frame(const frame& f, bool bottom) {
2646 #ifdef ASSERT
2647   LogTarget(Trace, continuations) lt;
2648   if (lt.develop_is_enabled()) {
2649     LogStream ls(lt);
2650     ls.print_cr("thawed frame:");
2651     print_frame_layout(f, false, &ls); // f.print_on(&ls);
2652   }
2653 #endif
2654 }
2655 
2656 inline void ThawBase::patch(frame& f, const frame& caller, bool bottom) {
2657   assert(!bottom || caller.fp() == _cont.entryFP(), "");
2658   if (bottom) {
2659     ContinuationHelper::Frame::patch_pc(caller, _cont.is_empty() ? caller.pc()
2660                                                                  : StubRoutines::cont_returnBarrier());
2661   } else if (_should_patch_caller_pc) {
2662     // Caller was deoptimized during thaw but we've overwritten the return address when copying f from the heap.
2663     // Also, on some platforms, if the caller is interpreted but the callee not we also need to patch.
2664 
2665 #if defined(PPC64) || defined(S390)
2666     assert(caller.is_deoptimized_frame() || caller.is_interpreted_frame(), "");
2667 #else
2668     assert(caller.is_deoptimized_frame(), "");
2669 #endif
2670 
2671     ContinuationHelper::Frame::patch_pc(caller, caller.raw_pc());
2672     _should_patch_caller_pc = false;
2673   }
2674 
2675   patch_pd(f, caller);
2676 
2677   if (f.is_interpreted_frame()) {
2678     ContinuationHelper::InterpretedFrame::patch_sender_sp(f, caller);
2679   }
2680 
2681   assert(!bottom || !_cont.is_empty() || Continuation::is_continuation_entry_frame(f, nullptr), "");
2682   assert(!bottom || (_cont.is_empty() != Continuation::is_cont_barrier_frame(f)), "");
2683   assert(!caller.is_compiled_frame() || verify_deopt_state(caller), "");
2684 }
2685 
2686 void ThawBase::clear_bitmap_bits(address start, address end) {
2687   assert(is_aligned(start, wordSize), "should be aligned: " PTR_FORMAT, p2i(start));
2688   assert(is_aligned(end, VMRegImpl::stack_slot_size), "should be aligned: " PTR_FORMAT, p2i(end));
2689 
2690   // we need to clear the bits that correspond to arguments as they reside in the caller frame
2691   // or they will keep objects that are otherwise unreachable alive.
2692 
2693   // Align `end` if UseCompressedOops is not set to avoid UB when calculating the bit index, since
2694   // `end` could be at an odd number of stack slots from `start`, i.e might not be oop aligned.
2695   // If that's the case the bit range corresponding to the last stack slot should not have bits set
2696   // anyways and we assert that before returning.
2697   address effective_end = UseCompressedOops ? end : align_down(end, wordSize);
2698   log_develop_trace(continuations)("clearing bitmap for " INTPTR_FORMAT " - " INTPTR_FORMAT, p2i(start), p2i(effective_end));
2699   stackChunkOop chunk = _cont.tail();
2700   chunk->bitmap().clear_range(chunk->bit_index_for(start), chunk->bit_index_for(effective_end));
2701   assert(effective_end == end || !chunk->bitmap().at(chunk->bit_index_for(effective_end)), "bit should not be set");
2702 }
2703 
2704 intptr_t* ThawBase::handle_preempted_continuation(intptr_t* sp, Continuation::preempt_kind preempt_kind, bool fast_case) {
2705   frame top(sp);
2706   assert(top.pc() == ContinuationHelper::return_address_at(sp - frame::sender_sp_ret_address_offset()), "");
2707   DEBUG_ONLY(verify_frame_kind(top, preempt_kind);)
2708   NOT_PRODUCT(int64_t tid = _thread->monitor_owner_id();)
2709 
2710   // Finish the VTMS transition.
2711   assert(_thread->is_in_vthread_transition(), "must be");
2712   bool is_vthread = Continuation::continuation_scope(_cont.continuation()) == java_lang_VirtualThread::vthread_scope();
2713   if (is_vthread) {
2714 #if INCLUDE_JVMTI
2715     if (MountUnmountDisabler::notify_jvmti_events()) {
2716       jvmti_mount_end(_thread, _cont, top, preempt_kind);
2717     } else
2718 #endif
2719     { // Faster version of MountUnmountDisabler::end_transition() to avoid
2720       // unnecessary extra instructions from jvmti_mount_end().
2721       java_lang_Thread::set_is_in_vthread_transition(_thread->vthread(), false);
2722       _thread->set_is_in_vthread_transition(false);
2723     }
2724   }
2725 
2726   if (fast_case) {
2727     // If we thawed in the slow path the runtime stub/native wrapper frame already
2728     // has the correct fp (see ThawBase::new_stack_frame). On the fast path though,
2729     // we copied the fp patched during freeze, which will now have to be fixed.
2730     assert(top.is_runtime_frame() || top.is_native_frame(), "");
2731     int fsize = top.cb()->frame_size();
2732     patch_pd(top, sp + fsize);
2733   }
2734 
2735   if (preempt_kind == Continuation::object_wait) {
2736     // Check now if we need to throw IE exception.
2737     bool throw_ie = _thread->pending_interrupted_exception();
2738     if (throw_ie) {
2739       throw_interrupted_exception(_thread, top);
2740       _thread->set_pending_interrupted_exception(false);
2741     }
2742     log_develop_trace(continuations, preempt)("Resuming " INT64_FORMAT" after preemption on Object.wait%s", tid, throw_ie ? "(throwing IE)" : "");
2743   } else if (preempt_kind == Continuation::monitorenter) {
2744     if (top.is_runtime_frame()) {
2745       // The continuation might now run on a different platform thread than the previous time so
2746       // we need to adjust the current thread saved in the stub frame before restoring registers.
2747       JavaThread** thread_addr = frame::saved_thread_address(top);
2748       if (thread_addr != nullptr) *thread_addr = _thread;
2749     }
2750     log_develop_trace(continuations, preempt)("Resuming " INT64_FORMAT " after preemption on monitorenter", tid);
2751   } else {
2752     // We need to redo the original call into the VM. First though, we need
2753     // to exit the monitor we just acquired (except on preemption cancelled
2754     // case where it was already released).
2755     assert(preempt_kind == Continuation::object_locker, "");
2756     if (_init_lock != nullptr) _init_lock->exit(_thread);
2757     sp = redo_vmcall(_thread, top);
2758   }
2759   return sp;
2760 }
2761 
2762 intptr_t* ThawBase::redo_vmcall(JavaThread* current, frame& top) {
2763   assert(!current->preempting(), "");
2764   NOT_PRODUCT(int64_t tid = current->monitor_owner_id();)
2765   intptr_t* sp = top.sp();
2766 
2767   {
2768     HandleMarkCleaner hmc(current);  // Cleanup all handles (including so._conth) before returning to Java.
2769     ContinuationWrapper::SafepointOp so(current, _cont);
2770     AnchorMark am(current, top);    // Set the anchor so that the stack is walkable.
2771 
2772     Method* m = top.interpreter_frame_method();
2773     Bytecode current_bytecode = Bytecode(m, top.interpreter_frame_bcp());
2774     Bytecodes::Code code = current_bytecode.code();
2775     log_develop_trace(continuations, preempt)("Redoing InterpreterRuntime::%s for " INT64_FORMAT, code == Bytecodes::Code::_new ? "_new" : "resolve_from_cache", tid);
2776 
2777     // These InterpreterRuntime entry points use JRT_ENTRY which uses a HandleMarkCleaner.
2778     // Create a HandeMark to avoid destroying so._conth.
2779     HandleMark hm(current);
2780     DEBUG_ONLY(JavaThread::AtRedoVMCall apvmc(current);)
2781     if (code == Bytecodes::Code::_new) {
2782       InterpreterRuntime::_new(current, m->constants(), current_bytecode.get_index_u2(code));
2783     } else {
2784       InterpreterRuntime::resolve_from_cache(current, code);
2785     }
2786   }
2787 
2788   if (current->preempting()) {
2789     // Preempted again so we just arrange to return to preempt stub to unmount.
2790     sp = push_preempt_adapter();
2791     current->set_preempt_alternate_return(nullptr);
2792     bool cancelled = current->preemption_cancelled();
2793     if (cancelled) {
2794       // Since preemption was cancelled, the thread will call thaw again from the preempt
2795       // stub. These retries could happen several times due to contention on the init_lock,
2796       // so just let the vthread umount to give a chance for other vthreads to run.
2797       current->set_preemption_cancelled(false);
2798       oop vthread = current->vthread();
2799       assert(java_lang_VirtualThread::state(vthread) == java_lang_VirtualThread::RUNNING, "wrong state for vthread");
2800       java_lang_VirtualThread::set_state(vthread, java_lang_VirtualThread::YIELDING);
2801 #if INCLUDE_JVMTI
2802       if (current->contended_entered_monitor() != nullptr) {
2803         current->set_contended_entered_monitor(nullptr);
2804       }
2805 #endif
2806     }
2807     log_develop_trace(continuations, preempt)("Preempted " INT64_FORMAT " again%s", tid, cancelled ? "(preemption cancelled, setting state to YIELDING)" : "");
2808   } else {
2809     log_develop_trace(continuations, preempt)("Call succesful, resuming " INT64_FORMAT, tid);
2810   }
2811   return sp;
2812 }
2813 
2814 void ThawBase::throw_interrupted_exception(JavaThread* current, frame& top) {
2815   HandleMarkCleaner hm(current);  // Cleanup all handles (including so._conth) before returning to Java.
2816   ContinuationWrapper::SafepointOp so(current, _cont);
2817   AnchorMark am(current, top);  // Set the anchor so that the stack is walkable.
2818   JRT_BLOCK
2819     THROW(vmSymbols::java_lang_InterruptedException());
2820   JRT_BLOCK_END
2821 }
2822 
2823 NOINLINE void ThawBase::recurse_thaw_interpreted_frame(const frame& hf, frame& caller, int num_frames, bool is_top) {
2824   assert(hf.is_interpreted_frame(), "");
2825 
2826   if (UNLIKELY(seen_by_gc())) {
2827     if (is_top && _process_args_at_top) {
2828       _cont.tail()->do_barriers<stackChunkOopDesc::BarrierType::Store>(_stream, SmallRegisterMap::instance_with_args());
2829     } else {
2830       _cont.tail()->do_barriers<stackChunkOopDesc::BarrierType::Store>(_stream, SmallRegisterMap::instance_no_args());
2831     }
2832   }
2833 
2834   const bool is_bottom_frame = recurse_thaw_java_frame<ContinuationHelper::InterpretedFrame>(caller, num_frames);
2835 
2836   DEBUG_ONLY(before_thaw_java_frame(hf, caller, is_bottom_frame, num_frames);)
2837 
2838   _align_size += frame::align_wiggle; // possible added alignment for internal interpreted frame alignment om AArch64
2839 
2840   frame f = new_stack_frame<ContinuationHelper::InterpretedFrame>(hf, caller, is_bottom_frame);
2841 
2842   intptr_t* const stack_frame_top = f.sp() + frame::metadata_words_at_top;
2843   intptr_t* const stack_frame_bottom = ContinuationHelper::InterpretedFrame::frame_bottom(f);
2844   intptr_t* const heap_frame_top = hf.unextended_sp() + frame::metadata_words_at_top;
2845   intptr_t* const heap_frame_bottom = ContinuationHelper::InterpretedFrame::frame_bottom(hf);
2846 
2847   assert(hf.is_heap_frame(), "should be");
2848   assert(!f.is_heap_frame(), "should not be");
2849 
2850   const int fsize = pointer_delta_as_int(heap_frame_bottom, heap_frame_top);
2851   assert((stack_frame_bottom == stack_frame_top + fsize), "");
2852 
2853   // Some architectures (like AArch64/PPC64/RISC-V) add padding between the locals and the fixed_frame to keep the fp 16-byte-aligned.
2854   // On those architectures we freeze the padding in order to keep the same fp-relative offsets in the fixed_frame.
2855   copy_from_chunk(heap_frame_top, stack_frame_top, fsize);
2856 
2857   // Make sure the relativized locals is already set.
2858   assert(f.interpreter_frame_local_at(0) == stack_frame_bottom - 1, "invalid frame bottom");
2859 
2860   derelativize_interpreted_frame_metadata(hf, f);
2861   patch(f, caller, is_bottom_frame);
2862 
2863   assert(f.is_interpreted_frame_valid(_cont.thread()), "invalid thawed frame");
2864   assert(stack_frame_bottom <= ContinuationHelper::Frame::frame_top(caller), "");
2865 
2866   CONT_JFR_ONLY(_jfr_info.record_interpreted_frame();)
2867 
2868   maybe_set_fastpath(f.sp());
2869 
2870   Method* m = hf.interpreter_frame_method();
2871   assert(!m->is_native() || !is_bottom_frame, "should be top frame of thaw_top case; missing caller frame");
2872   const int locals = m->max_locals();
2873 
2874   if (!is_bottom_frame) {
2875     // can only fix caller once this frame is thawed (due to callee saved regs)
2876     _cont.tail()->fix_thawed_frame(caller, SmallRegisterMap::instance_no_args());
2877   } else if (_cont.tail()->has_bitmap() && locals > 0) {
2878     assert(hf.is_heap_frame(), "should be");
2879     address start = (address)(heap_frame_bottom - locals);
2880     address end = (address)heap_frame_bottom;
2881     clear_bitmap_bits(start, end);
2882   }
2883 
2884   DEBUG_ONLY(after_thaw_java_frame(f, is_bottom_frame);)
2885   DEBUG_ONLY(address return_pc = ContinuationHelper::InterpretedFrame::return_pc(f);)
2886   assert(return_pc == _caller_raw_pc || (is_bottom_frame && return_pc == StubRoutines::cont_returnBarrier()), "wrong return pc");
2887   assert(f.pc() == f.raw_pc(), "");
2888   DEBUG_ONLY(_caller_raw_pc = f.pc();)
2889   caller = f;
2890 }
2891 
2892 void ThawBase::recurse_thaw_compiled_frame(const frame& hf, frame& caller, int num_frames, bool stub_caller) {
2893   assert(hf.is_compiled_frame(), "");
2894   assert(_preempted_case || !stub_caller, "stub caller not at preemption");
2895 
2896   if (!stub_caller && UNLIKELY(seen_by_gc())) { // recurse_thaw_stub_frame already invoked our barriers with a full regmap
2897     _cont.tail()->do_barriers<stackChunkOopDesc::BarrierType::Store>(_stream, SmallRegisterMap::instance_no_args());
2898   }
2899 
2900   const bool is_bottom_frame = recurse_thaw_java_frame<ContinuationHelper::CompiledFrame>(caller, num_frames);
2901 
2902   DEBUG_ONLY(before_thaw_java_frame(hf, caller, is_bottom_frame, num_frames);)
2903 
2904   assert(caller.sp() == caller.unextended_sp(), "");
2905 
2906   if ((!is_bottom_frame && caller.is_interpreted_frame()) || (is_bottom_frame && Interpreter::contains(_cont.tail()->pc()))) {
2907     _align_size += frame::align_wiggle; // we add one whether or not we've aligned because we add it in recurse_freeze_compiled_frame
2908   }
2909 
2910   int fsize = 0;
2911   int added_argsize = 0;
2912   bool augmented = hf.was_augmented_on_entry(fsize);
2913   if (!augmented) {
2914     added_argsize = (is_bottom_frame || caller.is_interpreted_frame()) ? hf.compiled_frame_stack_argsize() : 0;
2915     fsize += added_argsize;
2916   }
2917   assert(!is_bottom_frame || !augmented, "");
2918 
2919   // new_stack_frame must construct the resulting frame using hf.pc() rather than hf.raw_pc() because the frame is not
2920   // yet laid out in the stack, and so the original_pc is not stored in it.
2921   // As a result, f.is_deoptimized_frame() is always false and we must test hf to know if the frame is deoptimized.
2922   frame f = new_stack_frame<ContinuationHelper::CompiledFrame>(hf, caller, is_bottom_frame, augmented ? fsize - hf.cb()->frame_size() : 0);
2923   assert((int)(caller.sp() - f.sp()) == (augmented ? fsize : f.cb()->frame_size()), "");
2924 
2925   intptr_t* const stack_frame_top = f.sp();
2926   intptr_t* const heap_frame_top = hf.unextended_sp();
2927   intptr_t* from = heap_frame_top - frame::metadata_words_at_bottom;
2928   intptr_t* to   = stack_frame_top - frame::metadata_words_at_bottom;
2929   // copy metadata, except the metadata at the top of the (unextended) entry frame
2930   int sz = fsize + frame::metadata_words_at_bottom + (is_bottom_frame && added_argsize == 0 ? 0 : frame::metadata_words_at_top);
2931 
2932   // If we're the bottom-most thawed frame, we're writing to within one word from entrySP
2933   // (we might have one padding word for alignment)
2934   assert(!is_bottom_frame || (_cont.entrySP() - 1 <= to + sz && to + sz <= _cont.entrySP()), "");
2935   assert(!is_bottom_frame || hf.compiled_frame_stack_argsize() != 0 || (to + sz && to + sz == _cont.entrySP()), "");
2936 
2937   copy_from_chunk(from, to, sz); // copying good oops because we invoked barriers above
2938 
2939   patch(f, caller, is_bottom_frame);
2940 
2941   // f.is_deoptimized_frame() is always false and we must test hf.is_deoptimized_frame() (see comment above)
2942   assert(!f.is_deoptimized_frame(), "");
2943   if (hf.is_deoptimized_frame()) {
2944     maybe_set_fastpath(f.sp());
2945     f.set_deoptimized();
2946   } else if (_thread->is_interp_only_mode()
2947               || (stub_caller && f.cb()->as_nmethod()->is_marked_for_deoptimization())) {
2948     // The caller of the safepoint stub when the continuation is preempted is not at a call instruction, and so
2949     // cannot rely on nmethod patching for deopt.
2950     assert(_thread->is_interp_only_mode() || stub_caller, "expected a stub-caller");
2951 
2952     log_develop_trace(continuations)("Deoptimizing thawed frame");
2953     DEBUG_ONLY(ContinuationHelper::Frame::patch_pc(f, nullptr));
2954 
2955     f.deoptimize(nullptr); // the null thread simply avoids the assertion in deoptimize which we're not set up for
2956     assert(f.is_deoptimized_frame(), "");
2957     assert(ContinuationHelper::Frame::is_deopt_return(f.raw_pc(), f), "");
2958     maybe_set_fastpath(f.sp());
2959     assert(!_should_patch_caller_pc, "");
2960     _should_patch_caller_pc = true;
2961   }
2962 
2963   if (!is_bottom_frame) {
2964     // can only fix caller once this frame is thawed (due to callee saved regs); this happens on the stack
2965     _cont.tail()->fix_thawed_frame(caller, SmallRegisterMap::instance_no_args());
2966   } else if (_cont.tail()->has_bitmap() && added_argsize > 0) {
2967     address start = (address)(heap_frame_top + ContinuationHelper::CompiledFrame::size(hf) + frame::metadata_words_at_top);
2968     int stack_args_slots = f.cb()->as_nmethod()->num_stack_arg_slots(false /* rounded */);
2969     int argsize_in_bytes = stack_args_slots * VMRegImpl::stack_slot_size;
2970     clear_bitmap_bits(start, start + argsize_in_bytes);
2971   }
2972 
2973   DEBUG_ONLY(after_thaw_java_frame(f, is_bottom_frame);)
2974   DEBUG_ONLY(address return_pc = ContinuationHelper::CompiledFrame::return_pc(f);)
2975   assert(return_pc == _caller_raw_pc || (is_bottom_frame && return_pc == StubRoutines::cont_returnBarrier()), "wrong return pc");
2976   DEBUG_ONLY(_caller_raw_pc = f.raw_pc();)
2977   caller = f;
2978 }
2979 
2980 void ThawBase::recurse_thaw_stub_frame(const frame& hf, frame& caller, int num_frames) {
2981   DEBUG_ONLY(_frames++;)
2982 
2983   if (UNLIKELY(seen_by_gc())) {
2984     // Process the stub's caller here since we might need the full map.
2985     RegisterMap map(nullptr,
2986                     RegisterMap::UpdateMap::include,
2987                     RegisterMap::ProcessFrames::skip,
2988                     RegisterMap::WalkContinuation::skip);
2989     map.set_include_argument_oops(false);
2990     _stream.next(&map);
2991     assert(!_stream.is_done(), "");
2992     _cont.tail()->do_barriers<stackChunkOopDesc::BarrierType::Store>(_stream, &map);
2993   } else {
2994     _stream.next(SmallRegisterMap::instance_no_args());
2995     assert(!_stream.is_done(), "");
2996   }
2997 
2998   recurse_thaw_compiled_frame(_stream.to_frame(), caller, num_frames, true);
2999 
3000   assert(caller.is_compiled_frame(), "");
3001   assert(caller.sp() == caller.unextended_sp(), "");
3002 
3003   DEBUG_ONLY(before_thaw_java_frame(hf, caller, false /*is_bottom_frame*/, num_frames);)
3004 
3005   frame f = new_stack_frame<ContinuationHelper::StubFrame>(hf, caller, false);
3006   intptr_t* stack_frame_top = f.sp();
3007   intptr_t* heap_frame_top = hf.sp();
3008   int fsize = ContinuationHelper::StubFrame::size(hf);
3009 
3010   copy_from_chunk(heap_frame_top - frame::metadata_words, stack_frame_top - frame::metadata_words,
3011                   fsize + frame::metadata_words);
3012 
3013   patch(f, caller, false /*is_bottom_frame*/);
3014 
3015   // can only fix caller once this frame is thawed (due to callee saved regs)
3016   RegisterMap map(nullptr,
3017                   RegisterMap::UpdateMap::include,
3018                   RegisterMap::ProcessFrames::skip,
3019                   RegisterMap::WalkContinuation::skip);
3020   map.set_include_argument_oops(false);
3021   f.oop_map()->update_register_map(&f, &map);
3022   ContinuationHelper::update_register_map_with_callee(caller, &map);
3023   _cont.tail()->fix_thawed_frame(caller, &map);
3024 
3025   DEBUG_ONLY(after_thaw_java_frame(f, false /*is_bottom_frame*/);)
3026   assert(ContinuationHelper::StubFrame::return_pc(f) == _caller_raw_pc, "wrong return pc");
3027   caller = f;
3028 }
3029 
3030 void ThawBase::recurse_thaw_native_frame(const frame& hf, frame& caller, int num_frames) {
3031   assert(hf.is_native_frame(), "");
3032   assert(_preempted_case && hf.cb()->as_nmethod()->method()->is_object_wait0(), "");
3033 
3034   if (UNLIKELY(seen_by_gc())) { // recurse_thaw_stub_frame already invoked our barriers with a full regmap
3035     _cont.tail()->do_barriers<stackChunkOopDesc::BarrierType::Store>(_stream, SmallRegisterMap::instance_no_args());
3036   }
3037 
3038   const bool is_bottom_frame = recurse_thaw_java_frame<ContinuationHelper::NativeFrame>(caller, num_frames);
3039   assert(!is_bottom_frame, "");
3040 
3041   DEBUG_ONLY(before_thaw_java_frame(hf, caller, is_bottom_frame, num_frames);)
3042 
3043   assert(caller.sp() == caller.unextended_sp(), "");
3044 
3045   if (caller.is_interpreted_frame()) {
3046     _align_size += frame::align_wiggle; // we add one whether or not we've aligned because we add it in recurse_freeze_native_frame
3047   }
3048 
3049   // new_stack_frame must construct the resulting frame using hf.pc() rather than hf.raw_pc() because the frame is not
3050   // yet laid out in the stack, and so the original_pc is not stored in it.
3051   // As a result, f.is_deoptimized_frame() is always false and we must test hf to know if the frame is deoptimized.
3052   frame f = new_stack_frame<ContinuationHelper::NativeFrame>(hf, caller, false /* bottom */);
3053   intptr_t* const stack_frame_top = f.sp();
3054   intptr_t* const heap_frame_top = hf.unextended_sp();
3055 
3056   int fsize = ContinuationHelper::NativeFrame::size(hf);
3057   assert(fsize <= (int)(caller.unextended_sp() - f.unextended_sp()), "");
3058 
3059   intptr_t* from = heap_frame_top - frame::metadata_words_at_bottom;
3060   intptr_t* to   = stack_frame_top - frame::metadata_words_at_bottom;
3061   int sz = fsize + frame::metadata_words_at_bottom;
3062 
3063   copy_from_chunk(from, to, sz); // copying good oops because we invoked barriers above
3064 
3065   patch(f, caller, false /* bottom */);
3066 
3067   // f.is_deoptimized_frame() is always false and we must test hf.is_deoptimized_frame() (see comment above)
3068   assert(!f.is_deoptimized_frame(), "");
3069   assert(!hf.is_deoptimized_frame(), "");
3070   assert(!f.cb()->as_nmethod()->is_marked_for_deoptimization(), "");
3071 
3072   // can only fix caller once this frame is thawed (due to callee saved regs); this happens on the stack
3073   _cont.tail()->fix_thawed_frame(caller, SmallRegisterMap::instance_no_args());
3074 
3075   DEBUG_ONLY(after_thaw_java_frame(f, false /* bottom */);)
3076   assert(ContinuationHelper::NativeFrame::return_pc(f) == _caller_raw_pc, "wrong return pc");
3077   caller = f;
3078 }
3079 
3080 void ThawBase::finish_thaw(frame& f) {
3081   stackChunkOop chunk = _cont.tail();
3082 
3083   if (chunk->is_empty()) {
3084     // Only remove chunk from list if it can't be reused for another freeze
3085     if (seen_by_gc()) {
3086       _cont.set_tail(chunk->parent());
3087     } else {
3088       chunk->set_has_mixed_frames(false);
3089     }
3090     chunk->set_max_thawing_size(0);
3091   } else {
3092     chunk->set_max_thawing_size(chunk->max_thawing_size() - _align_size);
3093   }
3094   assert(chunk->is_empty() == (chunk->max_thawing_size() == 0), "");
3095 
3096   if (!is_aligned(f.sp(), frame::frame_alignment)) {
3097     assert(f.is_interpreted_frame(), "");
3098     f.set_sp(align_down(f.sp(), frame::frame_alignment));
3099   }
3100   push_return_frame(f);
3101    // can only fix caller after push_return_frame (due to callee saved regs)
3102   if (_process_args_at_top) {
3103     chunk->fix_thawed_frame(f, SmallRegisterMap::instance_with_args());
3104   } else {
3105     chunk->fix_thawed_frame(f, SmallRegisterMap::instance_no_args());
3106   }
3107 
3108   assert(_cont.is_empty() == _cont.last_frame().is_empty(), "");
3109 
3110   log_develop_trace(continuations)("thawed %d frames", _frames);
3111 
3112   LogTarget(Trace, continuations) lt;
3113   if (lt.develop_is_enabled()) {
3114     LogStream ls(lt);
3115     ls.print_cr("top hframe after (thaw):");
3116     _cont.last_frame().print_value_on(&ls);
3117   }
3118 }
3119 
3120 void ThawBase::push_return_frame(const frame& f) { // see generate_cont_thaw
3121   assert(!f.is_compiled_frame() || verify_deopt_state(f), "");
3122 
3123   LogTarget(Trace, continuations) lt;
3124   if (lt.develop_is_enabled()) {
3125     LogStream ls(lt);
3126     ls.print_cr("push_return_frame");
3127     f.print_value_on(&ls);
3128   }
3129 
3130   assert(f.sp() - frame::metadata_words_at_bottom >= _top_stack_address, "overwrote past thawing space"
3131     " to: " INTPTR_FORMAT " top_address: " INTPTR_FORMAT, p2i(f.sp() - frame::metadata_words), p2i(_top_stack_address));
3132   ContinuationHelper::Frame::patch_pc(f, f.raw_pc()); // in case we want to deopt the frame in a full transition, this is checked.
3133   ContinuationHelper::push_pd(f);
3134 
3135   assert(ContinuationHelper::Frame::assert_frame_laid_out(f), "");
3136 }
3137 
3138 // returns new top sp
3139 // called after preparations (stack overflow check and making room)
3140 template<typename ConfigT>
3141 static inline intptr_t* thaw_internal(JavaThread* thread, const Continuation::thaw_kind kind) {
3142   assert(thread == JavaThread::current(), "Must be current thread");
3143 
3144   CONT_JFR_ONLY(EventContinuationThaw event;)
3145 
3146   log_develop_trace(continuations)("~~~~ thaw kind: %d sp: " INTPTR_FORMAT, kind, p2i(thread->last_continuation()->entry_sp()));
3147 
3148   ContinuationEntry* entry = thread->last_continuation();
3149   assert(entry != nullptr, "");
3150   oop oopCont = entry->cont_oop(thread);
3151 
3152   assert(!jdk_internal_vm_Continuation::done(oopCont), "");
3153   assert(oopCont == get_continuation(thread), "");
3154   verify_continuation(oopCont);
3155 
3156   assert(entry->is_virtual_thread() == (entry->scope(thread) == java_lang_VirtualThread::vthread_scope()), "");
3157 
3158   ContinuationWrapper cont(thread, oopCont);
3159   log_develop_debug(continuations)("THAW #" INTPTR_FORMAT " " INTPTR_FORMAT, cont.hash(), p2i((oopDesc*)oopCont));
3160 
3161 #ifdef ASSERT
3162   set_anchor_to_entry(thread, cont.entry());
3163   log_frames(thread);
3164   clear_anchor(thread);
3165 #endif
3166 
3167   Thaw<ConfigT> thw(thread, cont);
3168   intptr_t* const sp = thw.thaw(kind);
3169   assert(is_aligned(sp, frame::frame_alignment), "");
3170   DEBUG_ONLY(log_frames_after_thaw(thread, cont, sp);)
3171 
3172   CONT_JFR_ONLY(thw.jfr_info().post_jfr_event(&event, cont.continuation(), thread);)
3173 
3174   verify_continuation(cont.continuation());
3175   log_develop_debug(continuations)("=== End of thaw #" INTPTR_FORMAT, cont.hash());
3176 
3177   return sp;
3178 }
3179 
3180 #ifdef ASSERT
3181 static void do_deopt_after_thaw(JavaThread* thread) {
3182   int i = 0;
3183   StackFrameStream fst(thread, true, false);
3184   fst.register_map()->set_include_argument_oops(false);
3185   ContinuationHelper::update_register_map_with_callee(*fst.current(), fst.register_map());
3186   for (; !fst.is_done(); fst.next()) {
3187     if (fst.current()->cb()->is_nmethod()) {
3188       nmethod* nm = fst.current()->cb()->as_nmethod();
3189       if (!nm->method()->is_continuation_native_intrinsic()) {
3190         nm->make_deoptimized();
3191       }
3192     }
3193   }
3194 }
3195 
3196 class ThawVerifyOopsClosure: public OopClosure {
3197   intptr_t* _p;
3198   outputStream* _st;
3199   bool is_good_oop(oop o) {
3200     return dbg_is_safe(o, -1) && dbg_is_safe(o->klass(), -1) && oopDesc::is_oop(o) && o->klass()->is_klass();
3201   }
3202 public:
3203   ThawVerifyOopsClosure(outputStream* st) : _p(nullptr), _st(st) {}
3204   intptr_t* p() { return _p; }
3205   void reset() { _p = nullptr; }
3206 
3207   virtual void do_oop(oop* p) {
3208     oop o = *p;
3209     if (o == nullptr || is_good_oop(o)) {
3210       return;
3211     }
3212     _p = (intptr_t*)p;
3213     _st->print_cr("*** non-oop " PTR_FORMAT " found at " PTR_FORMAT, p2i(*p), p2i(p));
3214   }
3215   virtual void do_oop(narrowOop* p) {
3216     oop o = RawAccess<>::oop_load(p);
3217     if (o == nullptr || is_good_oop(o)) {
3218       return;
3219     }
3220     _p = (intptr_t*)p;
3221     _st->print_cr("*** (narrow) non-oop %x found at " PTR_FORMAT, (int)(*p), p2i(p));
3222   }
3223 };
3224 
3225 static bool do_verify_after_thaw(JavaThread* thread, stackChunkOop chunk, outputStream* st) {
3226   assert(thread->has_last_Java_frame(), "");
3227 
3228   ResourceMark rm;
3229   ThawVerifyOopsClosure cl(st);
3230   NMethodToOopClosure cf(&cl, false);
3231 
3232   StackFrameStream fst(thread, true, false);
3233   fst.register_map()->set_include_argument_oops(false);
3234   ContinuationHelper::update_register_map_with_callee(*fst.current(), fst.register_map());
3235   for (; !fst.is_done() && !Continuation::is_continuation_enterSpecial(*fst.current()); fst.next()) {
3236     if (fst.current()->cb()->is_nmethod() && fst.current()->cb()->as_nmethod()->is_marked_for_deoptimization()) {
3237       st->print_cr(">>> do_verify_after_thaw deopt");
3238       fst.current()->deoptimize(nullptr);
3239       fst.current()->print_on(st);
3240     }
3241 
3242     fst.current()->oops_do(&cl, &cf, fst.register_map());
3243     if (cl.p() != nullptr) {
3244       frame fr = *fst.current();
3245       st->print_cr("Failed for frame barriers: %d",chunk->requires_barriers());
3246       fr.print_on(st);
3247       if (!fr.is_interpreted_frame()) {
3248         st->print_cr("size: %d argsize: %d",
3249                      ContinuationHelper::NonInterpretedUnknownFrame::size(fr),
3250                      ContinuationHelper::NonInterpretedUnknownFrame::stack_argsize(fr));
3251       }
3252       VMReg reg = fst.register_map()->find_register_spilled_here(cl.p(), fst.current()->sp());
3253       if (reg != nullptr) {
3254         st->print_cr("Reg %s %d", reg->name(), reg->is_stack() ? (int)reg->reg2stack() : -99);
3255       }
3256       cl.reset();
3257       DEBUG_ONLY(thread->print_frame_layout();)
3258       if (chunk != nullptr) {
3259         chunk->print_on(true, st);
3260       }
3261       return false;
3262     }
3263   }
3264   return true;
3265 }
3266 
3267 static bool verify_deopt_state(const frame& f) {
3268   nmethod* nm = f.cb()->as_nmethod();
3269   assert(f.is_deoptimized_frame() == nm->is_deopt_pc(f.raw_pc()), "");
3270   assert(f.is_deoptimized_frame() == (f.pc() != f.raw_pc()), "");
3271   assert(f.is_deoptimized_frame() == nm->is_deopt_pc(ContinuationHelper::Frame::real_pc(f)), "");
3272   return true;
3273 }
3274 
3275 static void log_frames(JavaThread* thread) {
3276   const static int show_entry_callers = 3;
3277   LogTarget(Trace, continuations) lt;
3278   if (!lt.develop_is_enabled()) {
3279     return;
3280   }
3281   LogStream ls(lt);
3282 
3283   ls.print_cr("------- frames --------- for thread " INTPTR_FORMAT, p2i(thread));
3284   if (!thread->has_last_Java_frame()) {
3285     ls.print_cr("NO ANCHOR!");
3286   }
3287 
3288   RegisterMap map(thread,
3289                   RegisterMap::UpdateMap::include,
3290                   RegisterMap::ProcessFrames::include,
3291                   RegisterMap::WalkContinuation::skip);
3292   map.set_include_argument_oops(false);
3293 
3294   if (false) {
3295     for (frame f = thread->last_frame(); !f.is_entry_frame(); f = f.sender(&map)) {
3296       f.print_on(&ls);
3297     }
3298   } else {
3299     map.set_skip_missing(true);
3300     ResetNoHandleMark rnhm;
3301     ResourceMark rm;
3302     HandleMark hm(Thread::current());
3303     FrameValues values;
3304 
3305     int i = 0;
3306     int post_entry = -1;
3307     for (frame f = thread->last_frame(); !f.is_first_frame(); f = f.sender(&map), i++) {
3308       f.describe(values, i, &map, i == 0);
3309       if (post_entry >= 0 || Continuation::is_continuation_enterSpecial(f))
3310         post_entry++;
3311       if (post_entry >= show_entry_callers)
3312         break;
3313     }
3314     values.print_on(thread, &ls);
3315   }
3316 
3317   ls.print_cr("======= end frames =========");
3318 }
3319 
3320 static void log_frames_after_thaw(JavaThread* thread, ContinuationWrapper& cont, intptr_t* sp) {
3321   intptr_t* sp0 = sp;
3322   bool preempted = false;
3323   stackChunkOop tail = cont.tail();
3324   if (tail != nullptr && tail->preempted()) {
3325     // Still preempted (monitor not acquired) so no frames were thawed.
3326     set_anchor(thread, cont.entrySP(), cont.entryPC());
3327     preempted = true;
3328   } else {
3329     set_anchor(thread, sp0);
3330   }
3331 
3332   log_frames(thread);
3333   if (LoomVerifyAfterThaw) {
3334     assert(do_verify_after_thaw(thread, cont.tail(), tty), "");
3335   }
3336   assert(preempted || ContinuationEntry::assert_entry_frame_laid_out(thread), "");
3337   clear_anchor(thread);
3338 
3339   LogTarget(Trace, continuations) lt;
3340   if (lt.develop_is_enabled()) {
3341     LogStream ls(lt);
3342     ls.print_cr("Jumping to frame (thaw):");
3343     frame(sp).print_value_on(&ls);
3344   }
3345 }
3346 #endif // ASSERT
3347 
3348 #include CPU_HEADER_INLINE(continuationFreezeThaw)
3349 
3350 #ifdef ASSERT
3351 static void print_frame_layout(const frame& f, bool callee_complete, outputStream* st) {
3352   ResourceMark rm;
3353   FrameValues values;
3354   assert(f.get_cb() != nullptr, "");
3355   RegisterMap map(f.is_heap_frame() ?
3356                     nullptr :
3357                     JavaThread::current(),
3358                   RegisterMap::UpdateMap::include,
3359                   RegisterMap::ProcessFrames::skip,
3360                   RegisterMap::WalkContinuation::skip);
3361   map.set_include_argument_oops(false);
3362   map.set_skip_missing(true);
3363   if (callee_complete) {
3364     frame::update_map_with_saved_link(&map, ContinuationHelper::Frame::callee_link_address(f));
3365   }
3366   const_cast<frame&>(f).describe(values, 0, &map, true);
3367   values.print_on(static_cast<JavaThread*>(nullptr), st);
3368 }
3369 #endif
3370 
3371 static address thaw_entry   = nullptr;
3372 static address freeze_entry = nullptr;
3373 static address freeze_preempt_entry = nullptr;
3374 
3375 address Continuation::thaw_entry() {
3376   return ::thaw_entry;
3377 }
3378 
3379 address Continuation::freeze_entry() {
3380   return ::freeze_entry;
3381 }
3382 
3383 address Continuation::freeze_preempt_entry() {
3384   return ::freeze_preempt_entry;
3385 }
3386 
3387 class ConfigResolve {
3388 public:
3389   static void resolve() { resolve_compressed(); }
3390 
3391   static void resolve_compressed() {
3392     UseCompressedOops ? resolve_gc<true>()
3393                       : resolve_gc<false>();
3394   }
3395 
3396 private:
3397   template <bool use_compressed>
3398   static void resolve_gc() {
3399     BarrierSet* bs = BarrierSet::barrier_set();
3400     assert(bs != nullptr, "freeze/thaw invoked before BarrierSet is set");
3401     switch (bs->kind()) {
3402 #define BARRIER_SET_RESOLVE_BARRIER_CLOSURE(bs_name)                    \
3403       case BarrierSet::bs_name: {                                       \
3404         resolve<use_compressed, typename BarrierSet::GetType<BarrierSet::bs_name>::type>(); \
3405       }                                                                 \
3406         break;
3407       FOR_EACH_BARRIER_SET_DO(BARRIER_SET_RESOLVE_BARRIER_CLOSURE)
3408 #undef BARRIER_SET_RESOLVE_BARRIER_CLOSURE
3409 
3410     default:
3411       fatal("BarrierSet resolving not implemented");
3412     };
3413   }
3414 
3415   template <bool use_compressed, typename BarrierSetT>
3416   static void resolve() {
3417     typedef Config<use_compressed ? oop_kind::NARROW : oop_kind::WIDE, BarrierSetT> SelectedConfigT;
3418 
3419     freeze_entry = (address)freeze<SelectedConfigT>;
3420     freeze_preempt_entry = (address)SelectedConfigT::freeze_preempt;
3421 
3422     // If we wanted, we could templatize by kind and have three different thaw entries
3423     thaw_entry   = (address)thaw<SelectedConfigT>;
3424   }
3425 };
3426 
3427 void Continuation::init() {
3428   ConfigResolve::resolve();
3429 }
--- EOF ---