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 <errno.h>
34 #include <pthread.h>
35 #include <signal.h>
36 #include <stdio.h>
37 #include <stdlib.h>
38
39 #if (__STDC_VERSION__ >= 199901L)
40 #include <stdbool.h>
41 #else
42 #define bool int
43 #define true 1
44 #define false 0
45 #endif
46
47 static struct sigaction sact[NSIG]; /* saved signal handlers */
48 static sigset_t jvmsigs; /* Signals used by jvm. */
49
50 #ifdef MACOSX
51 static __thread bool reentry = false; /* prevent reentry deadlock (per-thread) */
52 #endif
53
54 /* Used to synchronize the installation of signal handlers. */
55 static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
56 static pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
57 static pthread_t tid = 0;
58
59 typedef void (*sa_handler_t)(int);
60 typedef void (*sa_sigaction_t)(int, siginfo_t *, void *);
61 typedef sa_handler_t (*signal_function_t)(int, sa_handler_t);
62 typedef int (*sigaction_t)(int, const struct sigaction *, struct sigaction *);
63
64 static signal_function_t os_signal = 0; /* os's version of signal()/sigset() */
65 static sigaction_t os_sigaction = 0; /* os's version of sigaction() */
66
67 static bool jvm_signal_installing = false;
68 static bool jvm_signal_installed = false;
69
70 static void signal_lock() {
71 pthread_mutex_lock(&mutex);
72 /* When the jvm is installing its set of signal handlers, threads
73 * other than the jvm thread should wait. */
74 if (jvm_signal_installing) {
75 if (tid != pthread_self()) {
76 pthread_cond_wait(&cond, &mutex);
77 }
78 }
79 }
80
81 static void signal_unlock() {
82 pthread_mutex_unlock(&mutex);
83 }
84
85 static sa_handler_t call_os_signal(int sig, sa_handler_t disp,
86 bool is_sigset) {
87 sa_handler_t res;
88
89 if (os_signal == NULL) {
90 if (!is_sigset) {
91 os_signal = (signal_function_t)dlsym(RTLD_NEXT, "signal");
92 } else {
93 os_signal = (signal_function_t)dlsym(RTLD_NEXT, "sigset");
94 }
95 if (os_signal == NULL) {
96 printf("%s\n", dlerror());
97 exit(0);
98 }
99 }
100
101 #ifdef MACOSX
102 /* On macosx, the OS implementation of signal calls sigaction.
103 * Make sure we do not deadlock with ourself. (See JDK-8072147). */
104 reentry = true;
105 #endif
106
107 res = (*os_signal)(sig, disp);
108
109 #ifdef MACOSX
110 reentry = false;
111 #endif
112
113 return res;
114 }
115
116 static void save_signal_handler(int sig, sa_handler_t disp, bool is_sigset) {
117 sigset_t set;
118 sact[sig].sa_handler = disp;
119 sigemptyset(&set);
120 sact[sig].sa_mask = set;
121 if (!is_sigset) {
122 #ifdef SOLARIS
123 sact[sig].sa_flags = SA_NODEFER;
124 if (sig != SIGILL && sig != SIGTRAP && sig != SIGPWR) {
125 sact[sig].sa_flags |= SA_RESETHAND;
126 }
127 #else
128 sact[sig].sa_flags = 0;
129 #endif
130 } else {
131 sact[sig].sa_flags = 0;
132 }
133 }
134
135 static sa_handler_t set_signal(int sig, sa_handler_t disp, bool is_sigset) {
136 sa_handler_t oldhandler;
137 bool sigused;
138 bool sigblocked;
139
140 signal_lock();
141
142 sigused = sigismember(&jvmsigs, sig);
143 if (jvm_signal_installed && sigused) {
144 /* jvm has installed its signal handler for this signal. */
145 /* Save the handler. Don't really install it. */
146 if (is_sigset) {
147 sigblocked = sigismember(&(sact[sig].sa_mask), sig);
148 }
149 oldhandler = sact[sig].sa_handler;
150 save_signal_handler(sig, disp, is_sigset);
151
152 #ifdef SOLARIS
153 if (is_sigset && sigblocked) {
154 /* We won't honor the SIG_HOLD request to change the signal mask */
155 oldhandler = SIG_HOLD;
156 }
157 #endif
158
159 signal_unlock();
160 return oldhandler;
161 } else if (jvm_signal_installing) {
162 /* jvm is installing its signal handlers. Install the new
163 * handlers and save the old ones. jvm uses sigaction().
164 * Leave the piece here just in case. */
165 oldhandler = call_os_signal(sig, disp, is_sigset);
166 save_signal_handler(sig, oldhandler, is_sigset);
167
168 /* Record the signals used by jvm */
169 sigaddset(&jvmsigs, sig);
170
171 signal_unlock();
172 return oldhandler;
173 } else {
174 /* jvm has no relation with this signal (yet). Install the
175 * the handler. */
176 oldhandler = call_os_signal(sig, disp, is_sigset);
177
178 signal_unlock();
179 return oldhandler;
180 }
181 }
182
183 sa_handler_t signal(int sig, sa_handler_t disp) {
184 if (sig < 0 || sig >= NSIG) {
185 errno = EINVAL;
186 return SIG_ERR;
187 }
188
189 return set_signal(sig, disp, false);
190 }
191
192 sa_handler_t sigset(int sig, sa_handler_t disp) {
193 #ifdef _ALLBSD_SOURCE
194 printf("sigset() is not supported by BSD");
195 exit(0);
196 #else
197 if (sig < 0 || sig >= NSIG) {
198 errno = EINVAL;
199 return (sa_handler_t)-1;
200 }
201
202 return set_signal(sig, disp, true);
203 #endif
204 }
205
206 static int call_os_sigaction(int sig, const struct sigaction *act,
207 struct sigaction *oact) {
208 if (os_sigaction == NULL) {
209 os_sigaction = (sigaction_t)dlsym(RTLD_NEXT, "sigaction");
210 if (os_sigaction == NULL) {
211 printf("%s\n", dlerror());
212 exit(0);
213 }
214 }
215 return (*os_sigaction)(sig, act, oact);
216 }
217
218 int sigaction(int sig, const struct sigaction *act, struct sigaction *oact) {
219 int res;
220 bool sigused;
221 struct sigaction oldAct;
222
223 if (sig < 0 || sig >= NSIG) {
224 errno = EINVAL;
225 return -1;
226 }
227
228 #ifdef MACOSX
229 if (reentry) {
230 return call_os_sigaction(sig, act, oact);
231 }
232 #endif
233
234 signal_lock();
235
236 sigused = sigismember(&jvmsigs, sig);
237 if (jvm_signal_installed && sigused) {
238 /* jvm has installed its signal handler for this signal. */
239 /* Save the handler. Don't really install it. */
240 if (oact != NULL) {
241 *oact = sact[sig];
242 }
243 if (act != NULL) {
244 sact[sig] = *act;
245 }
246
247 signal_unlock();
248 return 0;
249 } else if (jvm_signal_installing) {
250 /* jvm is installing its signal handlers. Install the new
251 * handlers and save the old ones. */
252 res = call_os_sigaction(sig, act, &oldAct);
253 sact[sig] = oldAct;
254 if (oact != NULL) {
255 *oact = oldAct;
256 }
257
258 /* Record the signals used by jvm. */
259 sigaddset(&jvmsigs, sig);
260
261 signal_unlock();
262 return res;
263 } else {
264 /* jvm has no relation with this signal (yet). Install the
265 * the handler. */
266 res = call_os_sigaction(sig, act, oact);
267
268 signal_unlock();
269 return res;
270 }
271 }
272
273 /* The three functions for the jvm to call into. */
274 void JVM_begin_signal_setting() {
275 signal_lock();
276 sigemptyset(&jvmsigs);
277 jvm_signal_installing = true;
278 tid = pthread_self();
279 signal_unlock();
280 }
281
282 void JVM_end_signal_setting() {
283 signal_lock();
284 jvm_signal_installed = true;
285 jvm_signal_installing = false;
286 pthread_cond_broadcast(&cond);
287 signal_unlock();
288 }
289
290 struct sigaction *JVM_get_signal_action(int sig) {
291 /* Does race condition make sense here? */
292 if (sigismember(&jvmsigs, sig)) {
293 return &sact[sig];
294 }
295 return NULL;
296 }