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/threads.hpp"
 39 #include "runtime/threadWXSetters.inline.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 void BarrierSetNMethod::guard_with(nmethod* nm, int value) {
 79   assert((value & not_entrant) == 0, "not_entrant bit is reserved");
 80   set_guard_value(nm, value);
 81 }
 82 
 83 bool BarrierSetNMethod::is_armed(nmethod* nm) {
 84   return (guard_value(nm) & ~not_entrant) != disarmed_guard_value();
 85 }
 86 
 87 bool BarrierSetNMethod::nmethod_entry_barrier(nmethod* nm) {
 88   class OopKeepAliveClosure : public OopClosure {
 89   public:
 90     virtual void do_oop(oop* p) {
 91       // Loads on nmethod oops are phantom strength.
 92       //
 93       // Note that we could have used NativeAccess<ON_PHANTOM_OOP_REF>::oop_load(p),
 94       // but that would have *required* us to convert the returned LoadOopProxy to an oop,
 95       // or else keep alive load barrier will never be called. It's the LoadOopProxy-to-oop
 96       // conversion that performs the load barriers. This is too subtle, so we instead
 97       // perform an explicit keep alive call.
 98       oop obj = NativeAccess<ON_PHANTOM_OOP_REF | AS_NO_KEEPALIVE>::oop_load(p);
 99       if (obj != nullptr) {
100         Universe::heap()->keep_alive(obj);
101       }
102     }
103 
104     virtual void do_oop(narrowOop* p) { ShouldNotReachHere(); }
105   };
106 
107   if (!is_armed(nm)) {
108     // Some other thread got here first and healed the oops
109     // and disarmed the nmethod. No need to continue.
110     return true;
111   }
112 
113   MACOS_AARCH64_ONLY(ThreadWXEnable wx(WXWrite, Thread::current()));
114 
115   // If the nmethod is the only thing pointing to the oops, and we are using a
116   // SATB GC, then it is important that this code marks them live.
117   // Also, with concurrent GC, it is possible that frames in continuation stack
118   // chunks are not visited if they are allocated after concurrent GC started.
119   OopKeepAliveClosure cl;
120   nm->oops_do(&cl);
121 
122   // CodeCache unloading support
123   nm->mark_as_maybe_on_stack();
124 
125   disarm(nm);
126 
127   return true;
128 }
129 
130 int* BarrierSetNMethod::disarmed_guard_value_address() const {
131   return (int*) &_current_phase;
132 }
133 
134 ByteSize BarrierSetNMethod::thread_disarmed_guard_value_offset() const {
135   return Thread::nmethod_disarmed_guard_value_offset();
136 }
137 
138 class BarrierSetNMethodArmClosure : public ThreadClosure {
139 private:
140   int _disarmed_guard_value;
141 
142 public:
143   BarrierSetNMethodArmClosure(int disarmed_guard_value) :
144       _disarmed_guard_value(disarmed_guard_value) {}
145 
146   virtual void do_thread(Thread* thread) {
147     thread->set_nmethod_disarmed_guard_value(_disarmed_guard_value);
148   }
149 };
150 
151 void BarrierSetNMethod::arm_all_nmethods() {
152   // Change to a new global GC phase. Doing this requires changing the thread-local
153   // disarm value for all threads, to reflect the new GC phase.
154   // We wrap around at INT_MAX. That means that we assume nmethods won't have ABA
155   // problems in their nmethod disarm values after INT_MAX - 1 GCs. Every time a GC
156   // completes, ABA problems are removed, but if a concurrent GC is started and then
157   // aborted N times, that is when there could be ABA problems. If there are anything
158   // close to INT_MAX - 1 GCs starting without being able to finish, something is
159   // seriously wrong.
160   ++_current_phase;
161   if (_current_phase == INT_MAX) {
162     _current_phase = initial;
163   }
164   BarrierSetNMethodArmClosure cl(_current_phase);
165   Threads::threads_do(&cl);
166 
167 #if (defined(AARCH64) || defined(RISCV64)) && !defined(ZERO)
168   // We clear the patching epoch when disarming nmethods, so that
169   // the counter won't overflow.
170   BarrierSetAssembler::clear_patching_epoch();
171 #endif
172 }
173 
174 int BarrierSetNMethod::nmethod_stub_entry_barrier(address* return_address_ptr) {
175   address return_address = *return_address_ptr;
176   AARCH64_PORT_ONLY(return_address = pauth_strip_pointer(return_address));
177   CodeBlob* cb = CodeCache::find_blob(return_address);
178   assert(cb != nullptr, "invariant");
179 
180   nmethod* nm = cb->as_nmethod();
181   BarrierSetNMethod* bs_nm = BarrierSet::barrier_set()->barrier_set_nmethod();
182 
183   // Called upon first entry after being armed
184   bool may_enter = !bs_nm->is_not_entrant(nm) && bs_nm->nmethod_entry_barrier(nm);
185   assert(!nm->is_osr_method() || may_enter, "OSR nmethods should always be entrant after migration");
186 
187   if (may_enter) {
188     // In case a concurrent thread disarmed the nmethod, we need to ensure the new instructions
189     // are made visible, by using a cross modify fence. Note that this is synchronous cross modifying
190     // code, where the existence of new instructions is communicated via data (the guard value).
191     // This cross modify fence is only needed when the nmethod entry barrier modifies the
192     // instructions. Not all platforms currently do that, so if this check becomes expensive,
193     // it can be made conditional on the nmethod_patching_type.
194     OrderAccess::cross_modify_fence();
195 
196     // Diagnostic option to force deoptimization 1 in 10 times. It is otherwise
197     // a very rare event.
198     if (DeoptimizeNMethodBarriersALot && !nm->is_osr_method()) {
199       static volatile uint32_t counter=0;
200       if (AtomicAccess::add(&counter, 1u) % 10 == 0) {
201         may_enter = false;
202       }
203     }
204   }
205 
206   if (!may_enter) {
207     log_trace(nmethod, barrier)("Deoptimizing nmethod: " PTR_FORMAT, p2i(nm));
208     bs_nm->deoptimize(nm, return_address_ptr);
209   }
210   return may_enter ? 0 : 1;
211 }
212 
213 bool BarrierSetNMethod::nmethod_osr_entry_barrier(nmethod* nm) {
214   assert(nm->is_osr_method(), "Should not reach here");
215   log_trace(nmethod, barrier)("Running osr nmethod entry barrier: " PTR_FORMAT, p2i(nm));
216   bool result = nmethod_entry_barrier(nm);
217   OrderAccess::cross_modify_fence();
218   return result;
219 }
220 
221 oop BarrierSetNMethod::oop_load_no_keepalive(const nmethod* nm, int index) {
222   return NativeAccess<AS_NO_KEEPALIVE>::oop_load(nm->oop_addr_at(index));
223 }
224 
225 oop BarrierSetNMethod::oop_load_phantom(const nmethod* nm, int index) {
226   return NativeAccess<ON_PHANTOM_OOP_REF>::oop_load(nm->oop_addr_at(index));
227 }
228 
229 // Make the nmethod permanently not-entrant, so that nmethod_stub_entry_barrier() will call
230 // deoptimize() to redirect the caller to SharedRuntime::get_handle_wrong_method_stub().
231 // A sticky armed bit is set and other bits are preserved.  As a result, a call to
232 // nmethod_stub_entry_barrier() may appear to be spurious, because is_armed() still returns
233 // false and nmethod_entry_barrier() is not called.
234 void BarrierSetNMethod::make_not_entrant(nmethod* nm) {
235   set_guard_value(nm, not_entrant, not_entrant);
236 }
237 
238 bool BarrierSetNMethod::is_not_entrant(nmethod* nm) {
239   return (guard_value(nm) & not_entrant) != 0;
240 }