1 /*
2 * Copyright (c) 2001, 2010, 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 /* CopyrightVersion 1.2 */
26
27 /* This is a special library that should be loaded before libc &
28 * libthread to interpose the signal handler installation functions:
29 * sigaction(), signal(), sigset().
30 * Used for signal-chaining. See RFE 4381843.
31 */
32
33 #include <signal.h>
34 #include <dlfcn.h>
35 #include <pthread.h>
36 #include <stdio.h>
37 #include <stdlib.h>
38 #include <stdbool.h>
39
40 #define MAXSIGNUM 32
41 #define MASK(sig) ((unsigned int)1 << sig)
42
43 static struct sigaction sact[MAXSIGNUM]; /* saved signal handlers */
44 static unsigned int jvmsigs = 0; /* signals used by jvm */
45
46 /* used to synchronize the installation of signal handlers */
47 static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
48 static pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
49 static pthread_t tid = 0;
50
51 typedef void (*sa_handler_t)(int);
52 typedef void (*sa_sigaction_t)(int, siginfo_t *, void *);
53 typedef sa_handler_t (*signal_t)(int, sa_handler_t);
54 typedef int (*sigaction_t)(int, const struct sigaction *, struct sigaction *);
55
56 static signal_t os_signal = 0; /* os's version of signal()/sigset() */
57 static sigaction_t os_sigaction = 0; /* os's version of sigaction() */
58
59 static bool jvm_signal_installing = false;
60 static bool jvm_signal_installed = false;
61
62 static void signal_lock() {
63 pthread_mutex_lock(&mutex);
64 /* When the jvm is installing its set of signal handlers, threads
65 * other than the jvm thread should wait */
66 if (jvm_signal_installing) {
67 if (tid != pthread_self()) {
68 pthread_cond_wait(&cond, &mutex);
69 }
70 }
71 }
72
73 static void signal_unlock() {
74 pthread_mutex_unlock(&mutex);
75 }
76
77 static sa_handler_t call_os_signal(int sig, sa_handler_t disp,
78 bool is_sigset) {
79 if (os_signal == NULL) {
80 if (!is_sigset) {
81 os_signal = (signal_t)dlsym(RTLD_NEXT, "signal");
82 } else {
83 os_signal = (signal_t)dlsym(RTLD_NEXT, "sigset");
84 }
85 if (os_signal == NULL) {
86 printf("%s\n", dlerror());
87 exit(0);
88 }
89 }
90 return (*os_signal)(sig, disp);
91 }
92
93 static void save_signal_handler(int sig, sa_handler_t disp) {
94 sigset_t set;
95 sact[sig].sa_handler = disp;
96 sigemptyset(&set);
97 sact[sig].sa_mask = set;
98 sact[sig].sa_flags = 0;
99 }
100
101 static sa_handler_t set_signal(int sig, sa_handler_t disp, bool is_sigset) {
102 sa_handler_t oldhandler;
103 bool sigused;
104
105 signal_lock();
106
107 sigused = (MASK(sig) & jvmsigs) != 0;
108 if (jvm_signal_installed && sigused) {
109 /* jvm has installed its signal handler for this signal. */
110 /* Save the handler. Don't really install it. */
111 oldhandler = sact[sig].sa_handler;
112 save_signal_handler(sig, disp);
113
114 signal_unlock();
115 return oldhandler;
116 } else if (jvm_signal_installing) {
117 /* jvm is installing its signal handlers. Install the new
118 * handlers and save the old ones. jvm uses sigaction().
119 * Leave the piece here just in case. */
120 oldhandler = call_os_signal(sig, disp, is_sigset);
121 save_signal_handler(sig, oldhandler);
122
123 /* Record the signals used by jvm */
124 jvmsigs |= MASK(sig);
125
126 signal_unlock();
127 return oldhandler;
128 } else {
129 /* jvm has no relation with this signal (yet). Install the
130 * the handler. */
131 oldhandler = call_os_signal(sig, disp, is_sigset);
132
133 signal_unlock();
134 return oldhandler;
135 }
136 }
137
138 sa_handler_t signal(int sig, sa_handler_t disp) {
139 return set_signal(sig, disp, false);
140 }
141
142 sa_handler_t sigset(int sig, sa_handler_t disp) {
143 printf("sigset() is not supported by BSD");
144 exit(0);
145 }
146
147 static int call_os_sigaction(int sig, const struct sigaction *act,
148 struct sigaction *oact) {
149 if (os_sigaction == NULL) {
150 os_sigaction = (sigaction_t)dlsym(RTLD_NEXT, "sigaction");
151 if (os_sigaction == NULL) {
152 printf("%s\n", dlerror());
153 exit(0);
154 }
155 }
156 return (*os_sigaction)(sig, act, oact);
157 }
158
159 int sigaction(int sig, const struct sigaction *act, struct sigaction *oact) {
160 int res;
161 bool sigused;
162 struct sigaction oldAct;
163
164 signal_lock();
165
166 sigused = (MASK(sig) & jvmsigs) != 0;
167 if (jvm_signal_installed && sigused) {
168 /* jvm has installed its signal handler for this signal. */
169 /* Save the handler. Don't really install it. */
170 if (oact != NULL) {
171 *oact = sact[sig];
172 }
173 if (act != NULL) {
174 sact[sig] = *act;
175 }
176
177 signal_unlock();
178 return 0;
179 } else if (jvm_signal_installing) {
180 /* jvm is installing its signal handlers. Install the new
181 * handlers and save the old ones. */
182 res = call_os_sigaction(sig, act, &oldAct);
183 sact[sig] = oldAct;
184 if (oact != NULL) {
185 *oact = oldAct;
186 }
187
188 /* Record the signals used by jvm */
189 jvmsigs |= MASK(sig);
190
191 signal_unlock();
192 return res;
193 } else {
194 /* jvm has no relation with this signal (yet). Install the
195 * the handler. */
196 res = call_os_sigaction(sig, act, oact);
197
198 signal_unlock();
199 return res;
200 }
201 }
202
203 /* The three functions for the jvm to call into */
204 void JVM_begin_signal_setting() {
205 signal_lock();
206 jvm_signal_installing = true;
207 tid = pthread_self();
208 signal_unlock();
209 }
210
211 void JVM_end_signal_setting() {
212 signal_lock();
213 jvm_signal_installed = true;
214 jvm_signal_installing = false;
215 pthread_cond_broadcast(&cond);
216 signal_unlock();
217 }
218
219 struct sigaction *JVM_get_signal_action(int sig) {
220 /* Does race condition make sense here? */
221 if ((MASK(sig) & jvmsigs) != 0) {
222 return &sact[sig];
223 }
224 return NULL;
225 }