1 /*
  2  * Copyright (c) 2018, 2025, Oracle and/or its affiliates. All rights reserved.
  3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  4  *
  5  * This code is free software; you can redistribute it and/or modify it
  6  * under the terms of the GNU General Public License version 2 only, as
  7  * published by the Free Software Foundation.
  8  *
  9  * This code is distributed in the hope that it will be useful, but WITHOUT
 10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 12  * version 2 for more details (a copy is included in the LICENSE file that
 13  * accompanied this code).
 14  *
 15  * You should have received a copy of the GNU General Public License version
 16  * 2 along with this work; if not, write to the Free Software Foundation,
 17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 18  *
 19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 20  * or visit www.oracle.com if you need additional information or have any
 21  * questions.
 22  *
 23  */
 24 
 25 #include "code/codeCache.hpp"
 26 #include "code/nmethod.hpp"
 27 #include "gc/shared/barrierSet.hpp"
 28 #include "gc/shared/barrierSetAssembler.hpp"
 29 #include "gc/shared/barrierSetNMethod.hpp"
 30 #include "gc/shared/collectedHeap.hpp"
 31 #include "logging/log.hpp"
 32 #include "memory/iterator.hpp"
 33 #include "memory/universe.hpp"
 34 #include "oops/access.inline.hpp"
 35 #include "oops/method.inline.hpp"
 36 #include "runtime/frame.inline.hpp"
 37 #include "runtime/javaThread.hpp"
 38 #include "runtime/threadWXSetters.inline.hpp"
 39 #include "runtime/threads.hpp"
 40 #include "utilities/debug.hpp"
 41 #if INCLUDE_JVMCI
 42 #include "jvmci/jvmciRuntime.hpp"
 43 #endif
 44 
 45 int BarrierSetNMethod::disarmed_guard_value() const {
 46   return *disarmed_guard_value_address();
 47 }
 48 
 49 bool BarrierSetNMethod::supports_entry_barrier(nmethod* nm) {
 50   if (nm->method()->is_method_handle_intrinsic()) {
 51     return false;
 52   }
 53 
 54   if (nm->method()->is_continuation_enter_intrinsic()) {
 55     return false;
 56   }
 57 
 58   if (nm->method()->is_continuation_yield_intrinsic()) {
 59     return false;
 60   }
 61 
 62   if (nm->method()->is_continuation_native_intrinsic()) {
 63     guarantee(false, "Unknown Continuation native intrinsic");
 64     return false;
 65   }
 66 
 67   if (nm->is_native_method() || nm->is_compiled_by_c2() || nm->is_compiled_by_c1() || nm->is_compiled_by_jvmci()) {
 68     return true;
 69   }
 70 
 71   return false;
 72 }
 73 
 74 void BarrierSetNMethod::disarm(nmethod* nm) {
 75   set_guard_value(nm, disarmed_guard_value());
 76 }
 77 
 78 bool BarrierSetNMethod::is_armed(nmethod* nm) {
 79   return guard_value(nm) != disarmed_guard_value();
 80 }
 81 
 82 bool BarrierSetNMethod::nmethod_entry_barrier(nmethod* nm) {
 83   class OopKeepAliveClosure : public OopClosure {
 84   public:
 85     virtual void do_oop(oop* p) {
 86       // Loads on nmethod oops are phantom strength.
 87       //
 88       // Note that we could have used NativeAccess<ON_PHANTOM_OOP_REF>::oop_load(p),
 89       // but that would have *required* us to convert the returned LoadOopProxy to an oop,
 90       // or else keep alive load barrier will never be called. It's the LoadOopProxy-to-oop
 91       // conversion that performs the load barriers. This is too subtle, so we instead
 92       // perform an explicit keep alive call.
 93       oop obj = NativeAccess<ON_PHANTOM_OOP_REF | AS_NO_KEEPALIVE>::oop_load(p);
 94       if (obj != nullptr) {
 95         Universe::heap()->keep_alive(obj);
 96       }
 97     }
 98 
 99     virtual void do_oop(narrowOop* p) { ShouldNotReachHere(); }
100   };
101 
102   if (!is_armed(nm)) {
103     // Some other thread got here first and healed the oops
104     // and disarmed the nmethod. No need to continue.
105     return true;
106   }
107 
108   // If the nmethod is the only thing pointing to the oops, and we are using a
109   // SATB GC, then it is important that this code marks them live.
110   // Also, with concurrent GC, it is possible that frames in continuation stack
111   // chunks are not visited if they are allocated after concurrent GC started.
112   OopKeepAliveClosure cl;
113   nm->oops_do(&cl);
114 
115   // CodeCache unloading support
116   nm->mark_as_maybe_on_stack();
117 
118   disarm(nm);
119 
120   return true;
121 }
122 
123 int* BarrierSetNMethod::disarmed_guard_value_address() const {
124   return (int*) &_current_phase;
125 }
126 
127 ByteSize BarrierSetNMethod::thread_disarmed_guard_value_offset() const {
128   return Thread::nmethod_disarmed_guard_value_offset();
129 }
130 
131 class BarrierSetNMethodArmClosure : public ThreadClosure {
132 private:
133   int _disarmed_guard_value;
134 
135 public:
136   BarrierSetNMethodArmClosure(int disarmed_guard_value) :
137       _disarmed_guard_value(disarmed_guard_value) {}
138 
139   virtual void do_thread(Thread* thread) {
140     thread->set_nmethod_disarmed_guard_value(_disarmed_guard_value);
141   }
142 };
143 
144 void BarrierSetNMethod::arm_all_nmethods() {
145   // Change to a new global GC phase. Doing this requires changing the thread-local
146   // disarm value for all threads, to reflect the new GC phase.
147   // We wrap around at INT_MAX. That means that we assume nmethods won't have ABA
148   // problems in their nmethod disarm values after INT_MAX - 1 GCs. Every time a GC
149   // completes, ABA problems are removed, but if a concurrent GC is started and then
150   // aborted N times, that is when there could be ABA problems. If there are anything
151   // close to INT_MAX - 1 GCs starting without being able to finish, something is
152   // seriously wrong.
153   ++_current_phase;
154   if (_current_phase == INT_MAX) {
155     _current_phase = 1;
156   }
157   BarrierSetNMethodArmClosure cl(_current_phase);
158   Threads::threads_do(&cl);
159 
160 #if (defined(AARCH64) || defined(RISCV64)) && !defined(ZERO)
161   // We clear the patching epoch when disarming nmethods, so that
162   // the counter won't overflow.
163   BarrierSetAssembler::clear_patching_epoch();
164 #endif
165 }
166 
167 int BarrierSetNMethod::nmethod_stub_entry_barrier(address* return_address_ptr) {
168   // Enable WXWrite: the function is called directly from nmethod_entry_barrier
169   // stub.
170   MACOS_AARCH64_ONLY(ThreadWXEnable wx(WXWrite, Thread::current()));
171 
172   address return_address = *return_address_ptr;
173   AARCH64_PORT_ONLY(return_address = pauth_strip_pointer(return_address));
174   CodeBlob* cb = CodeCache::find_blob(return_address);
175   assert(cb != nullptr, "invariant");
176 
177   nmethod* nm = cb->as_nmethod();
178   BarrierSetNMethod* bs_nm = BarrierSet::barrier_set()->barrier_set_nmethod();
179 
180   // Called upon first entry after being armed
181   bool may_enter = bs_nm->nmethod_entry_barrier(nm);
182   assert(!nm->is_osr_method() || may_enter, "OSR nmethods should always be entrant after migration");
183 
184   // In case a concurrent thread disarmed the nmethod, we need to ensure the new instructions
185   // are made visible, by using a cross modify fence. Note that this is synchronous cross modifying
186   // code, where the existence of new instructions is communicated via data (the guard value).
187   // This cross modify fence is only needed when the nmethod entry barrier modifies the
188   // instructions. Not all platforms currently do that, so if this check becomes expensive,
189   // it can be made conditional on the nmethod_patching_type.
190   OrderAccess::cross_modify_fence();
191 
192   // Diagnostic option to force deoptimization 1 in 10 times. It is otherwise
193   // a very rare event.
194   if (DeoptimizeNMethodBarriersALot && !nm->is_osr_method()) {
195     static volatile uint32_t counter=0;
196     if (Atomic::add(&counter, 1u) % 10 == 0) {
197       may_enter = false;
198     }
199   }
200 
201   if (!may_enter) {
202     log_trace(nmethod, barrier)("Deoptimizing nmethod: " PTR_FORMAT, p2i(nm));
203     bs_nm->deoptimize(nm, return_address_ptr);
204   }
205   return may_enter ? 0 : 1;
206 }
207 
208 bool BarrierSetNMethod::nmethod_osr_entry_barrier(nmethod* nm) {
209   assert(nm->is_osr_method(), "Should not reach here");
210   log_trace(nmethod, barrier)("Running osr nmethod entry barrier: " PTR_FORMAT, p2i(nm));
211   bool result = nmethod_entry_barrier(nm);
212   OrderAccess::cross_modify_fence();
213   return result;
214 }