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 }