1 /*
2 * Copyright (c) 2001, 2018, Oracle and/or its affiliates. All rights reserved.
3 * Copyright (c) 2012, 2015 SAP SE. All rights reserved.
4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
5 *
6 * This code is free software; you can redistribute it and/or modify it
7 * under the terms of the GNU General Public License version 2 only, as
8 * published by the Free Software Foundation.
9 *
10 * This code is distributed in the hope that it will be useful, but WITHOUT
11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
13 * version 2 for more details (a copy is included in the LICENSE file that
14 * accompanied this code).
15 *
16 * You should have received a copy of the GNU General Public License version
17 * 2 along with this work; if not, write to the Free Software Foundation,
18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
19 *
20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
21 * or visit www.oracle.com if you need additional information or have any
22 * questions.
23 *
24 */
25
26 /* This is a special library that should be loaded before libc &
27 * libthread to interpose the signal handler installation functions:
28 * sigaction(), signal(), sigset().
29 * Used for signal-chaining. See RFE 4381843.
30 */
31
32 #include <dlfcn.h>
33 #include <pthread.h>
34 #include <signal.h>
35 #include <stdio.h>
36 #include <stdlib.h>
37
38 #if (__STDC_VERSION__ >= 199901L)
39 #include <stdbool.h>
40 #else
41 #define bool int
42 #define true 1
43 #define false 0
44 #endif
45
46 static struct sigaction sact[NSIG]; /* saved signal handlers */
47 static sigset_t jvmsigs; /* Signals used by jvm. */
48
49 #ifdef MACOSX
50 static __thread bool reentry = false; /* prevent reentry deadlock (per-thread) */
51 #endif
52
53 /* Used to synchronize the installation of signal handlers. */
54 static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
55 static pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
56 static pthread_t tid = 0;
57
58 typedef void (*sa_handler_t)(int);
59 typedef void (*sa_sigaction_t)(int, siginfo_t *, void *);
60 typedef sa_handler_t (*signal_function_t)(int, sa_handler_t);
61 typedef int (*sigaction_t)(int, const struct sigaction *, struct sigaction *);
62
63 static signal_function_t os_signal = 0; /* os's version of signal()/sigset() */
64 static sigaction_t os_sigaction = 0; /* os's version of sigaction() */
65
66 static bool jvm_signal_installing = false;
67 static bool jvm_signal_installed = false;
68
69 static void signal_lock() {
70 pthread_mutex_lock(&mutex);
71 /* When the jvm is installing its set of signal handlers, threads
72 * other than the jvm thread should wait. */
73 if (jvm_signal_installing) {
74 if (tid != pthread_self()) {
75 pthread_cond_wait(&cond, &mutex);
76 }
77 }
78 }
79
80 static void signal_unlock() {
81 pthread_mutex_unlock(&mutex);
82 }
83
84 static sa_handler_t call_os_signal(int sig, sa_handler_t disp,
85 bool is_sigset) {
86 sa_handler_t res;
87
88 if (os_signal == NULL) {
89 if (!is_sigset) {
90 os_signal = (signal_function_t)dlsym(RTLD_NEXT, "signal");
91 } else {
92 os_signal = (signal_function_t)dlsym(RTLD_NEXT, "sigset");
93 }
94 if (os_signal == NULL) {
95 printf("%s\n", dlerror());
96 exit(0);
97 }
98 }
99
100 #ifdef MACOSX
101 /* On macosx, the OS implementation of signal calls sigaction.
102 * Make sure we do not deadlock with ourself. (See JDK-8072147). */
103 reentry = true;
104 #endif
105
106 res = (*os_signal)(sig, disp);
107
108 #ifdef MACOSX
109 reentry = false;
110 #endif
111
112 return res;
113 }
114
115 static void save_signal_handler(int sig, sa_handler_t disp, bool is_sigset) {
116 sigset_t set;
117 sact[sig].sa_handler = disp;
118 sigemptyset(&set);
119 sact[sig].sa_mask = set;
120 if (!is_sigset) {
121 #ifdef SOLARIS
122 sact[sig].sa_flags = SA_NODEFER;
123 if (sig != SIGILL && sig != SIGTRAP && sig != SIGPWR) {
124 sact[sig].sa_flags |= SA_RESETHAND;
125 }
126 #else
127 sact[sig].sa_flags = 0;
128 #endif
129 } else {
130 sact[sig].sa_flags = 0;
131 }
132 }
133
134 static sa_handler_t set_signal(int sig, sa_handler_t disp, bool is_sigset) {
135 sa_handler_t oldhandler;
136 bool sigused;
137 bool sigblocked;
138
139 signal_lock();
140
141 sigused = sigismember(&jvmsigs, sig);
142 if (jvm_signal_installed && sigused) {
143 /* jvm has installed its signal handler for this signal. */
144 /* Save the handler. Don't really install it. */
145 if (is_sigset) {
146 sigblocked = sigismember(&(sact[sig].sa_mask), sig);
147 }
148 oldhandler = sact[sig].sa_handler;
149 save_signal_handler(sig, disp, is_sigset);
150
151 #ifdef SOLARIS
152 if (is_sigset && sigblocked) {
153 /* We won't honor the SIG_HOLD request to change the signal mask */
154 oldhandler = SIG_HOLD;
155 }
156 #endif
157
158 signal_unlock();
159 return oldhandler;
160 } else if (jvm_signal_installing) {
161 /* jvm is installing its signal handlers. Install the new
162 * handlers and save the old ones. jvm uses sigaction().
163 * Leave the piece here just in case. */
164 oldhandler = call_os_signal(sig, disp, is_sigset);
165 save_signal_handler(sig, oldhandler, is_sigset);
166
167 /* Record the signals used by jvm */
168 sigaddset(&jvmsigs, sig);
169
170 signal_unlock();
171 return oldhandler;
172 } else {
173 /* jvm has no relation with this signal (yet). Install the
174 * the handler. */
175 oldhandler = call_os_signal(sig, disp, is_sigset);
176
177 signal_unlock();
178 return oldhandler;
179 }
180 }
181
182 sa_handler_t signal(int sig, sa_handler_t disp) {
183 return set_signal(sig, disp, false);
184 }
185
186 sa_handler_t sigset(int sig, sa_handler_t disp) {
187 #ifdef _ALLBSD_SOURCE
188 printf("sigset() is not supported by BSD");
189 exit(0);
190 #else
191 return set_signal(sig, disp, true);
192 #endif
193 }
194
195 static int call_os_sigaction(int sig, const struct sigaction *act,
196 struct sigaction *oact) {
197 if (os_sigaction == NULL) {
198 os_sigaction = (sigaction_t)dlsym(RTLD_NEXT, "sigaction");
199 if (os_sigaction == NULL) {
200 printf("%s\n", dlerror());
201 exit(0);
202 }
203 }
204 return (*os_sigaction)(sig, act, oact);
205 }
206
207 int sigaction(int sig, const struct sigaction *act, struct sigaction *oact) {
208 int res;
209 bool sigused;
210 struct sigaction oldAct;
211
212 #ifdef MACOSX
213 if (reentry) {
214 return call_os_sigaction(sig, act, oact);
215 }
216 #endif
217
218 signal_lock();
219
220 sigused = sigismember(&jvmsigs, sig);
221 if (jvm_signal_installed && sigused) {
222 /* jvm has installed its signal handler for this signal. */
223 /* Save the handler. Don't really install it. */
224 if (oact != NULL) {
225 *oact = sact[sig];
226 }
227 if (act != NULL) {
228 sact[sig] = *act;
229 }
230
231 signal_unlock();
232 return 0;
233 } else if (jvm_signal_installing) {
234 /* jvm is installing its signal handlers. Install the new
235 * handlers and save the old ones. */
236 res = call_os_sigaction(sig, act, &oldAct);
237 sact[sig] = oldAct;
238 if (oact != NULL) {
239 *oact = oldAct;
240 }
241
242 /* Record the signals used by jvm. */
243 sigaddset(&jvmsigs, sig);
244
245 signal_unlock();
246 return res;
247 } else {
248 /* jvm has no relation with this signal (yet). Install the
249 * the handler. */
250 res = call_os_sigaction(sig, act, oact);
251
252 signal_unlock();
253 return res;
254 }
255 }
256
257 /* The three functions for the jvm to call into. */
258 void JVM_begin_signal_setting() {
259 signal_lock();
260 sigemptyset(&jvmsigs);
261 jvm_signal_installing = true;
262 tid = pthread_self();
263 signal_unlock();
264 }
265
266 void JVM_end_signal_setting() {
267 signal_lock();
268 jvm_signal_installed = true;
269 jvm_signal_installing = false;
270 pthread_cond_broadcast(&cond);
271 signal_unlock();
272 }
273
274 struct sigaction *JVM_get_signal_action(int sig) {
275 /* Does race condition make sense here? */
276 if (sigismember(&jvmsigs, sig)) {
277 return &sact[sig];
278 }
279 return NULL;
280 }