1 /*
2 * Copyright (c) 2018, 2023, 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 "precompiled.hpp"
26 #include "code/codeCache.hpp"
27 #include "code/nmethod.hpp"
28 #include "gc/shared/barrierSet.hpp"
29 #include "gc/shared/barrierSetAssembler.hpp"
30 #include "gc/shared/barrierSetNMethod.hpp"
31 #include "gc/shared/collectedHeap.hpp"
32 #include "logging/log.hpp"
33 #include "memory/iterator.hpp"
34 #include "memory/universe.hpp"
35 #include "oops/access.inline.hpp"
36 #include "oops/method.inline.hpp"
37 #include "runtime/frame.inline.hpp"
38 #include "runtime/javaThread.hpp"
39 #include "runtime/threadWXSetters.inline.hpp"
40 #include "runtime/threads.hpp"
41 #include "utilities/debug.hpp"
42 #if INCLUDE_JVMCI
43 #include "jvmci/jvmciRuntime.hpp"
44 #endif
45
46 int BarrierSetNMethod::disarmed_guard_value() const {
47 return *disarmed_guard_value_address();
48 }
49
50 bool BarrierSetNMethod::supports_entry_barrier(nmethod* nm) {
51 if (nm->method()->is_method_handle_intrinsic()) {
52 return false;
53 }
54
55 if (nm->method()->is_continuation_enter_intrinsic()) {
56 return false;
57 }
58
59 if (nm->method()->is_continuation_yield_intrinsic()) {
60 return false;
61 }
62
63 if (nm->method()->is_continuation_native_intrinsic()) {
64 guarantee(false, "Unknown Continuation native intrinsic");
65 return false;
66 }
67
68 if (nm->is_native_method() || nm->is_compiled_by_c2() || nm->is_compiled_by_c1() || nm->is_compiled_by_jvmci()) {
69 return true;
70 }
71
72 return false;
73 }
74
75 void BarrierSetNMethod::disarm(nmethod* nm) {
76 set_guard_value(nm, disarmed_guard_value());
77 }
78
79 bool BarrierSetNMethod::is_armed(nmethod* nm) {
80 return guard_value(nm) != disarmed_guard_value();
81 }
82
83 bool BarrierSetNMethod::nmethod_entry_barrier(nmethod* nm) {
84 class OopKeepAliveClosure : public OopClosure {
85 public:
86 virtual void do_oop(oop* p) {
87 // Loads on nmethod oops are phantom strength.
88 //
89 // Note that we could have used NativeAccess<ON_PHANTOM_OOP_REF>::oop_load(p),
90 // but that would have *required* us to convert the returned LoadOopProxy to an oop,
91 // or else keep alive load barrier will never be called. It's the LoadOopProxy-to-oop
92 // conversion that performs the load barriers. This is too subtle, so we instead
93 // perform an explicit keep alive call.
94 oop obj = NativeAccess<ON_PHANTOM_OOP_REF | AS_NO_KEEPALIVE>::oop_load(p);
95 if (obj != nullptr) {
96 Universe::heap()->keep_alive(obj);
97 }
98 }
99
100 virtual void do_oop(narrowOop* p) { ShouldNotReachHere(); }
101 };
102
103 if (!is_armed(nm)) {
104 // Some other thread got here first and healed the oops
105 // and disarmed the nmethod. No need to continue.
106 return true;
107 }
108
109 // If the nmethod is the only thing pointing to the oops, and we are using a
110 // SATB GC, then it is important that this code marks them live.
111 // Also, with concurrent GC, it is possible that frames in continuation stack
112 // chunks are not visited if they are allocated after concurrent GC started.
113 OopKeepAliveClosure cl;
114 nm->oops_do(&cl);
115
116 // CodeCache unloading support
117 nm->mark_as_maybe_on_stack();
118
119 disarm(nm);
120
121 return true;
122 }
123
124 int* BarrierSetNMethod::disarmed_guard_value_address() const {
125 return (int*) &_current_phase;
126 }
127
128 ByteSize BarrierSetNMethod::thread_disarmed_guard_value_offset() const {
129 return Thread::nmethod_disarmed_guard_value_offset();
130 }
131
132 class BarrierSetNMethodArmClosure : public ThreadClosure {
133 private:
134 int _disarmed_guard_value;
135
136 public:
137 BarrierSetNMethodArmClosure(int disarmed_guard_value) :
138 _disarmed_guard_value(disarmed_guard_value) {}
139
140 virtual void do_thread(Thread* thread) {
141 thread->set_nmethod_disarmed_guard_value(_disarmed_guard_value);
142 }
143 };
144
145 void BarrierSetNMethod::arm_all_nmethods() {
146 // Change to a new global GC phase. Doing this requires changing the thread-local
147 // disarm value for all threads, to reflect the new GC phase.
148 // We wrap around at INT_MAX. That means that we assume nmethods won't have ABA
149 // problems in their nmethod disarm values after INT_MAX - 1 GCs. Every time a GC
150 // completes, ABA problems are removed, but if a concurrent GC is started and then
151 // aborted N times, that is when there could be ABA problems. If there are anything
152 // close to INT_MAX - 1 GCs starting without being able to finish, something is
153 // seriously wrong.
154 ++_current_phase;
155 if (_current_phase == INT_MAX) {
156 _current_phase = 1;
157 }
158 BarrierSetNMethodArmClosure cl(_current_phase);
159 Threads::threads_do(&cl);
160
161 #if (defined(AARCH64) || defined(RISCV64)) && !defined(ZERO)
162 // We clear the patching epoch when disarming nmethods, so that
163 // the counter won't overflow.
164 BarrierSetAssembler::clear_patching_epoch();
165 #endif
166 }
167
168 int BarrierSetNMethod::nmethod_stub_entry_barrier(address* return_address_ptr) {
169 // Enable WXWrite: the function is called directly from nmethod_entry_barrier
170 // stub.
171 MACOS_AARCH64_ONLY(ThreadWXEnable wx(WXWrite, Thread::current()));
172
173 address return_address = *return_address_ptr;
174 AARCH64_PORT_ONLY(return_address = pauth_strip_pointer(return_address));
175 CodeBlob* cb = CodeCache::find_blob(return_address);
176 assert(cb != nullptr, "invariant");
177
178 nmethod* nm = cb->as_nmethod();
179 BarrierSetNMethod* bs_nm = BarrierSet::barrier_set()->barrier_set_nmethod();
180
181 // Called upon first entry after being armed
182 bool may_enter = bs_nm->nmethod_entry_barrier(nm);
183 assert(!nm->is_osr_method() || may_enter, "OSR nmethods should always be entrant after migration");
184
185 // In case a concurrent thread disarmed the nmethod, we need to ensure the new instructions
186 // are made visible, by using a cross modify fence. Note that this is synchronous cross modifying
187 // code, where the existence of new instructions is communicated via data (the guard value).
188 // This cross modify fence is only needed when the nmethod entry barrier modifies the
189 // instructions. Not all platforms currently do that, so if this check becomes expensive,
190 // it can be made conditional on the nmethod_patching_type.
191 OrderAccess::cross_modify_fence();
192
193 // Diagnostic option to force deoptimization 1 in 10 times. It is otherwise
194 // a very rare event.
195 if (DeoptimizeNMethodBarriersALot && !nm->is_osr_method()) {
196 static volatile uint32_t counter=0;
197 if (Atomic::add(&counter, 1u) % 10 == 0) {
198 may_enter = false;
199 }
200 }
201
202 if (!may_enter) {
203 log_trace(nmethod, barrier)("Deoptimizing nmethod: " PTR_FORMAT, p2i(nm));
204 bs_nm->deoptimize(nm, return_address_ptr);
205 }
206 return may_enter ? 0 : 1;
207 }
208
209 bool BarrierSetNMethod::nmethod_osr_entry_barrier(nmethod* nm) {
210 assert(nm->is_osr_method(), "Should not reach here");
211 log_trace(nmethod, barrier)("Running osr nmethod entry barrier: " PTR_FORMAT, p2i(nm));
212 bool result = nmethod_entry_barrier(nm);
213 OrderAccess::cross_modify_fence();
214 return result;
215 }