8338383: Implement JEP 491: Synchronize Virtual Threads without Pinning

Co-authored-by: Patricio Chilano Mateo <[email protected]>
Co-authored-by: Alan Bateman <[email protected]>
Co-authored-by: Andrew Haley <[email protected]>
Co-authored-by: Fei Yang <[email protected]>
Co-authored-by: Coleen Phillimore <[email protected]>
Co-authored-by: Richard Reingruber <[email protected]>
Co-authored-by: Martin Doerr <[email protected]>
Reviewed-by: aboldtch, dholmes, coleenp, fbredberg, dlong, sspitsyn

Author: 7 people

src/hotspot/cpu/aarch64/aarch64.ad

@@ -1648,8 +1648,8 @@ int MachCallRuntimeNode::ret_addr_offset() {
   // for real runtime callouts it will be six instructions
   // see aarch64_enc_java_to_runtime
   //   adr(rscratch2, retaddr)
+  //   str(rscratch2, Address(rthread, JavaThread::last_Java_pc_offset()));
   //   lea(rscratch1, RuntimeAddress(addr)
-  //   stp(zr, rscratch2, Address(__ pre(sp, -2 * wordSize)))
   //   blr(rscratch1)
   CodeBlob *cb = CodeCache::find_blob(_entry_point);
   if (cb) {
@@ -3696,14 +3696,13 @@ encode %{
       __ post_call_nop();
     } else {
       Label retaddr;
+      // Make the anchor frame walkable
       __ adr(rscratch2, retaddr);
+      __ str(rscratch2, Address(rthread, JavaThread::last_Java_pc_offset()));
       __ lea(rscratch1, RuntimeAddress(entry));
-      // Leave a breadcrumb for JavaFrameAnchor::capture_last_Java_pc()
-      __ stp(zr, rscratch2, Address(__ pre(sp, -2 * wordSize)));
       __ blr(rscratch1);
       __ bind(retaddr);
       __ post_call_nop();
-      __ add(sp, sp, 2 * wordSize);
     }
     if (Compile::current()->max_vector_size() > 0) {
       __ reinitialize_ptrue();

src/hotspot/cpu/aarch64/c1_MacroAssembler_aarch64.cpp

@@ -119,8 +119,8 @@ int C1_MacroAssembler::lock_object(Register hdr, Register obj, Register disp_hdr
     cbnz(hdr, slow_case);
     // done
     bind(done);
+    inc_held_monitor_count(rscratch1);
   }
-  increment(Address(rthread, JavaThread::held_monitor_count_offset()));
   return null_check_offset;
 }
 
@@ -159,8 +159,8 @@ void C1_MacroAssembler::unlock_object(Register hdr, Register obj, Register disp_
     }
     // done
     bind(done);
+    dec_held_monitor_count(rscratch1);
   }
-  decrement(Address(rthread, JavaThread::held_monitor_count_offset()));
 }
 
 

src/hotspot/cpu/aarch64/c1_Runtime1_aarch64.cpp

@@ -160,16 +160,15 @@ int StubAssembler::call_RT(Register oop_result1, Register metadata_result, addre
 }
 
 enum return_state_t {
-  does_not_return, requires_return
+  does_not_return, requires_return, requires_pop_epilogue_return
 };
 
-
 // Implementation of StubFrame
 
 class StubFrame: public StackObj {
  private:
   StubAssembler* _sasm;
-  bool _return_state;
+  return_state_t _return_state;
 
  public:
   StubFrame(StubAssembler* sasm, const char* name, bool must_gc_arguments, return_state_t return_state=requires_return);
@@ -183,8 +182,17 @@ void StubAssembler::prologue(const char* name, bool must_gc_arguments) {
   enter();
 }
 
-void StubAssembler::epilogue() {
-  leave();
+void StubAssembler::epilogue(bool use_pop) {
+  // Avoid using a leave instruction when this frame may
+  // have been frozen, since the current value of rfp
+  // restored from the stub would be invalid. We still
+  // must restore the rfp value saved on enter though.
+  if (use_pop) {
+    ldp(rfp, lr, Address(post(sp, 2 * wordSize)));
+    authenticate_return_address();
+  } else {
+    leave();
+  }
   ret(lr);
 }
 
@@ -203,10 +211,10 @@ void StubFrame::load_argument(int offset_in_words, Register reg) {
 }
 
 StubFrame::~StubFrame() {
-  if (_return_state == requires_return) {
-    __ epilogue();
-  } else {
+  if (_return_state == does_not_return) {
     __ should_not_reach_here();
+  } else {
+    __ epilogue(_return_state == requires_pop_epilogue_return);
   }
 }
 
@@ -252,7 +260,7 @@ static OopMap* generate_oop_map(StubAssembler* sasm, bool save_fpu_registers) {
 
   for (int i = 0; i < FrameMap::nof_cpu_regs; i++) {
     Register r = as_Register(i);
-    if (i <= 18 && i != rscratch1->encoding() && i != rscratch2->encoding()) {
+    if (r == rthread || (i <= 18 && i != rscratch1->encoding() && i != rscratch2->encoding())) {
       int sp_offset = cpu_reg_save_offsets[i];
       oop_map->set_callee_saved(VMRegImpl::stack2reg(sp_offset),
                                 r->as_VMReg());
@@ -337,6 +345,15 @@ void Runtime1::initialize_pd() {
   }
 }
 
+// return: offset in 64-bit words.
+uint Runtime1::runtime_blob_current_thread_offset(frame f) {
+  CodeBlob* cb = f.cb();
+  assert(cb == Runtime1::blob_for(C1StubId::monitorenter_id) ||
+         cb == Runtime1::blob_for(C1StubId::monitorenter_nofpu_id), "must be");
+  assert(cb != nullptr && cb->is_runtime_stub(), "invalid frame");
+  int offset = cpu_reg_save_offsets[rthread->encoding()];
+  return offset / 2;   // SP offsets are in halfwords
+}
 
 // target: the entry point of the method that creates and posts the exception oop
 // has_argument: true if the exception needs arguments (passed in rscratch1 and rscratch2)
@@ -868,7 +885,7 @@ OopMapSet* Runtime1::generate_code_for(C1StubId id, StubAssembler* sasm) {
       // fall through
     case C1StubId::monitorenter_id:
       {
-        StubFrame f(sasm, "monitorenter", dont_gc_arguments);
+        StubFrame f(sasm, "monitorenter", dont_gc_arguments, requires_pop_epilogue_return);
         OopMap* map = save_live_registers(sasm, save_fpu_registers);
 
         // Called with store_parameter and not C abi

src/hotspot/cpu/aarch64/c2_MacroAssembler_aarch64.cpp

@@ -153,7 +153,7 @@ void C2_MacroAssembler::fast_lock(Register objectReg, Register boxReg, Register
   Label count, no_count;
 
   assert(LockingMode != LM_LIGHTWEIGHT, "lightweight locking should use fast_lock_lightweight");
-  assert_different_registers(oop, box, tmp, disp_hdr);
+  assert_different_registers(oop, box, tmp, disp_hdr, rscratch2);
 
   // Load markWord from object into displaced_header.
   ldr(disp_hdr, Address(oop, oopDesc::mark_offset_in_bytes()));
@@ -206,12 +206,10 @@ void C2_MacroAssembler::fast_lock(Register objectReg, Register boxReg, Register
   // Handle existing monitor.
   bind(object_has_monitor);
 
-  // The object's monitor m is unlocked iff m->owner == nullptr,
-  // otherwise m->owner may contain a thread or a stack address.
-  //
-  // Try to CAS m->owner from null to current thread.
+  // Try to CAS owner (no owner => current thread's _lock_id).
+  ldr(rscratch2, Address(rthread, JavaThread::lock_id_offset()));
   add(tmp, disp_hdr, (in_bytes(ObjectMonitor::owner_offset())-markWord::monitor_value));
-  cmpxchg(tmp, zr, rthread, Assembler::xword, /*acquire*/ true,
+  cmpxchg(tmp, zr, rscratch2, Assembler::xword, /*acquire*/ true,
           /*release*/ true, /*weak*/ false, tmp3Reg); // Sets flags for result
 
   // Store a non-null value into the box to avoid looking like a re-entrant
@@ -223,7 +221,7 @@ void C2_MacroAssembler::fast_lock(Register objectReg, Register boxReg, Register
 
   br(Assembler::EQ, cont); // CAS success means locking succeeded
 
-  cmp(tmp3Reg, rthread);
+  cmp(tmp3Reg, rscratch2);
   br(Assembler::NE, cont); // Check for recursive locking
 
   // Recursive lock case
@@ -236,7 +234,9 @@ void C2_MacroAssembler::fast_lock(Register objectReg, Register boxReg, Register
   br(Assembler::NE, no_count);
 
   bind(count);
-  increment(Address(rthread, JavaThread::held_monitor_count_offset()));
+  if (LockingMode == LM_LEGACY) {
+    inc_held_monitor_count(rscratch1);
+  }
 
   bind(no_count);
 }
@@ -343,15 +343,17 @@ void C2_MacroAssembler::fast_unlock(Register objectReg, Register boxReg, Registe
   br(Assembler::NE, no_count);
 
   bind(count);
-  decrement(Address(rthread, JavaThread::held_monitor_count_offset()));
+  if (LockingMode == LM_LEGACY) {
+    dec_held_monitor_count(rscratch1);
+  }
 
   bind(no_count);
 }
 
 void C2_MacroAssembler::fast_lock_lightweight(Register obj, Register box, Register t1,
                                               Register t2, Register t3) {
   assert(LockingMode == LM_LIGHTWEIGHT, "must be");
-  assert_different_registers(obj, box, t1, t2, t3);
+  assert_different_registers(obj, box, t1, t2, t3, rscratch2);
 
   // Handle inflated monitor.
   Label inflated;
@@ -467,13 +469,14 @@ void C2_MacroAssembler::fast_lock_lightweight(Register obj, Register box, Regist
     // Compute owner address.
     lea(t2_owner_addr, owner_address);
 
-    // CAS owner (null => current thread).
-    cmpxchg(t2_owner_addr, zr, rthread, Assembler::xword, /*acquire*/ true,
+    // Try to CAS owner (no owner => current thread's _lock_id).
+    ldr(rscratch2, Address(rthread, JavaThread::lock_id_offset()));
+    cmpxchg(t2_owner_addr, zr, rscratch2, Assembler::xword, /*acquire*/ true,
             /*release*/ false, /*weak*/ false, t3_owner);
     br(Assembler::EQ, monitor_locked);
 
     // Check if recursive.
-    cmp(t3_owner, rthread);
+    cmp(t3_owner, rscratch2);
     br(Assembler::NE, slow_path);
 
     // Recursive.
@@ -486,7 +489,6 @@ void C2_MacroAssembler::fast_lock_lightweight(Register obj, Register box, Regist
   }
 
   bind(locked);
-  increment(Address(rthread, JavaThread::held_monitor_count_offset()));
 
 #ifdef ASSERT
   // Check that locked label is reached with Flags == EQ.
@@ -655,7 +657,6 @@ void C2_MacroAssembler::fast_unlock_lightweight(Register obj, Register box, Regi
   }
 
   bind(unlocked);
-  decrement(Address(rthread, JavaThread::held_monitor_count_offset()));
   cmp(zr, zr); // Set Flags to EQ => fast path
 
 #ifdef ASSERT

src/hotspot/cpu/aarch64/continuationFreezeThaw_aarch64.inline.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2019, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -129,6 +129,11 @@ void FreezeBase::adjust_interpreted_frame_unextended_sp(frame& f) {
   }
 }
 
+inline void FreezeBase::prepare_freeze_interpreted_top_frame(frame& f) {
+  assert(f.interpreter_frame_last_sp() == nullptr, "should be null for top frame");
+  f.interpreter_frame_set_last_sp(f.unextended_sp());
+}
+
 inline void FreezeBase::relativize_interpreted_frame_metadata(const frame& f, const frame& hf) {
   assert(hf.fp() == hf.unextended_sp() + (f.fp() - f.unextended_sp()), "");
   assert((f.at(frame::interpreter_frame_last_sp_offset) != 0)
@@ -149,10 +154,16 @@ inline void FreezeBase::relativize_interpreted_frame_metadata(const frame& f, co
   // extended_sp is already relativized by TemplateInterpreterGenerator::generate_normal_entry or
   // AbstractInterpreter::layout_activation
 
+  // The interpreter native wrapper code adds space in the stack equal to size_of_parameters()
+  // after the fixed part of the frame. For wait0 this is equal to 3 words (this + long parameter).
+  // We adjust by this size since otherwise the saved last sp will be less than the extended_sp.
+  DEBUG_ONLY(Method* m = hf.interpreter_frame_method();)
+  DEBUG_ONLY(int extra_space = m->is_object_wait0() ? m->size_of_parameters() : 0;)
+
   assert((hf.fp() - hf.unextended_sp()) == (f.fp() - f.unextended_sp()), "");
   assert(hf.unextended_sp() == (intptr_t*)hf.at(frame::interpreter_frame_last_sp_offset), "");
   assert(hf.unextended_sp() <= (intptr_t*)hf.at(frame::interpreter_frame_initial_sp_offset), "");
-  assert(hf.unextended_sp() >  (intptr_t*)hf.at(frame::interpreter_frame_extended_sp_offset), "");
+  assert(hf.unextended_sp() + extra_space >  (intptr_t*)hf.at(frame::interpreter_frame_extended_sp_offset), "");
   assert(hf.fp()            >  (intptr_t*)hf.at(frame::interpreter_frame_initial_sp_offset), "");
   assert(hf.fp()            <= (intptr_t*)hf.at(frame::interpreter_frame_locals_offset), "");
 }
@@ -213,7 +224,6 @@ template<typename FKind> frame ThawBase::new_stack_frame(const frame& hf, frame&
     // If caller is interpreted it already made room for the callee arguments
     int overlap = caller.is_interpreted_frame() ? ContinuationHelper::InterpretedFrame::stack_argsize(hf) : 0;
     const int fsize = (int)(ContinuationHelper::InterpretedFrame::frame_bottom(hf) - hf.unextended_sp() - overlap);
-    const int locals = hf.interpreter_frame_method()->max_locals();
     intptr_t* frame_sp = caller.unextended_sp() - fsize;
     intptr_t* fp = frame_sp + (hf.fp() - heap_sp);
     if ((intptr_t)fp % frame::frame_alignment != 0) {
@@ -235,7 +245,7 @@ template<typename FKind> frame ThawBase::new_stack_frame(const frame& hf, frame&
     int fsize = FKind::size(hf);
     intptr_t* frame_sp = caller.unextended_sp() - fsize;
     if (bottom || caller.is_interpreted_frame()) {
-      int argsize = hf.compiled_frame_stack_argsize();
+      int argsize = FKind::stack_argsize(hf);
 
       fsize += argsize;
       frame_sp   -= argsize;
@@ -252,8 +262,8 @@ template<typename FKind> frame ThawBase::new_stack_frame(const frame& hf, frame&
       // we need to recreate a "real" frame pointer, pointing into the stack
       fp = frame_sp + FKind::size(hf) - frame::sender_sp_offset;
     } else {
-      fp = FKind::stub
-        ? frame_sp + fsize - frame::sender_sp_offset // on AArch64, this value is used for the safepoint stub
+      fp = FKind::stub || FKind::native
+        ? frame_sp + fsize - frame::sender_sp_offset // fp always points to the address below the pushed return pc. We need correct address.
         : *(intptr_t**)(hf.sp() - frame::sender_sp_offset); // we need to re-read fp because it may be an oop and we might have fixed the frame.
     }
     return frame(frame_sp, frame_sp, fp, hf.pc(), hf.cb(), hf.oop_map(), false); // TODO PERF : this computes deopt state; is it necessary?
@@ -277,6 +287,22 @@ inline void ThawBase::patch_pd(frame& f, const frame& caller) {
   patch_callee_link(caller, caller.fp());
 }
 
+inline void ThawBase::patch_pd(frame& f, intptr_t* caller_sp) {
+  intptr_t* fp = caller_sp - frame::sender_sp_offset;
+  patch_callee_link(f, fp);
+}
+
+inline intptr_t* ThawBase::push_cleanup_continuation() {
+  frame enterSpecial = new_entry_frame();
+  intptr_t* sp = enterSpecial.sp();
+
+  sp[-1] = (intptr_t)ContinuationEntry::cleanup_pc();
+  sp[-2] = (intptr_t)enterSpecial.fp();
+
+  log_develop_trace(continuations, preempt)("push_cleanup_continuation initial sp: " INTPTR_FORMAT " final sp: " INTPTR_FORMAT, p2i(sp + 2 * frame::metadata_words), p2i(sp));
+  return sp;
+}
+
 inline void ThawBase::derelativize_interpreted_frame_metadata(const frame& hf, const frame& f) {
   // Make sure that last_sp is kept relativized.
   assert((intptr_t*)f.at_relative(frame::interpreter_frame_last_sp_offset) == f.unextended_sp(), "");
@@ -285,7 +311,9 @@ inline void ThawBase::derelativize_interpreted_frame_metadata(const frame& hf, c
   assert(f.at_absolute(frame::interpreter_frame_monitor_block_top_offset) <= frame::interpreter_frame_initial_sp_offset, "");
 
   // Make sure that extended_sp is kept relativized.
-  assert((intptr_t*)f.at_relative(frame::interpreter_frame_extended_sp_offset) < f.unextended_sp(), "");
+  DEBUG_ONLY(Method* m = hf.interpreter_frame_method();)
+  DEBUG_ONLY(int extra_space = m->is_object_wait0() ? m->size_of_parameters() : 0;) // see comment in relativize_interpreted_frame_metadata()
+  assert((intptr_t*)f.at_relative(frame::interpreter_frame_extended_sp_offset) < f.unextended_sp() + extra_space, "");
 }
 
 #endif // CPU_AARCH64_CONTINUATIONFREEZETHAW_AARCH64_INLINE_HPP

src/hotspot/cpu/aarch64/continuationHelper_aarch64.inline.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2022, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -40,6 +40,22 @@ static inline intptr_t** link_address(const frame& f) {
             : (intptr_t**)(f.unextended_sp() + f.cb()->frame_size() - frame::sender_sp_offset);
 }
 
+static inline void patch_return_pc_with_preempt_stub(frame& f) {
+  if (f.is_runtime_frame()) {
+    // Unlike x86 we don't know where in the callee frame the return pc is
+    // saved so we can't patch the return from the VM call back to Java.
+    // Instead, we will patch the return from the runtime stub back to the
+    // compiled method so that the target returns to the preempt cleanup stub.
+    intptr_t* caller_sp = f.sp() + f.cb()->frame_size();
+    caller_sp[-1] = (intptr_t)StubRoutines::cont_preempt_stub();
+  } else {
+    // The target will check for preemption once it returns to the interpreter
+    // or the native wrapper code and will manually jump to the preempt stub.
+    JavaThread *thread = JavaThread::current();
+    thread->set_preempt_alternate_return(StubRoutines::cont_preempt_stub());
+  }
+}
+
 inline int ContinuationHelper::frame_align_words(int size) {
 #ifdef _LP64
   return size & 1;
@@ -83,12 +99,12 @@ inline void ContinuationHelper::set_anchor_to_entry_pd(JavaFrameAnchor* anchor,
   anchor->set_last_Java_fp(entry->entry_fp());
 }
 
-#ifdef ASSERT
 inline void ContinuationHelper::set_anchor_pd(JavaFrameAnchor* anchor, intptr_t* sp) {
   intptr_t* fp = *(intptr_t**)(sp - frame::sender_sp_offset);
   anchor->set_last_Java_fp(fp);
 }
 
+#ifdef ASSERT
 inline bool ContinuationHelper::Frame::assert_frame_laid_out(frame f) {
   intptr_t* sp = f.sp();
   address pc = ContinuationHelper::return_address_at(