1 /*
2 * Copyright (c) 2001, 2013, 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 <stdint.h>
39
40 #define bool int
41 #define true 1
42 #define false 0
43
44 #define MASK(sig) ((uint64_t)1 << (sig-1)) // 0 is not a signal.
45 // Check whether all signals fit into jvmsigs. -1 as MASK shifts by -1.
46 #if (64 < NSIG-1)
47 #error "Not all signals can be encoded in jvmsigs. Adapt its type!"
48 #endif
49 static struct sigaction sact[NSIG]; /* saved signal handlers */
50 static uint64_t jvmsigs = 0; /* signals used by jvm */
51
52 /* used to synchronize the installation of signal handlers */
53 static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
54 static pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
55 static pthread_t tid = 0;
56
57 typedef void (*sa_handler_t)(int);
58 typedef void (*sa_sigaction_t)(int, siginfo_t *, void *);
59 typedef sa_handler_t (*signal_t)(int, sa_handler_t);
60 typedef int (*sigaction_t)(int, const struct sigaction *, struct sigaction *);
61
62 static signal_t os_signal = 0; /* os's version of signal()/sigset() */
63 static sigaction_t os_sigaction = 0; /* os's version of sigaction() */
64
65 static bool jvm_signal_installing = false;
66 static bool jvm_signal_installed = false;
67
68 static void signal_lock() {
69 pthread_mutex_lock(&mutex);
70 /* When the jvm is installing its set of signal handlers, threads
71 * other than the jvm thread should wait */
72 if (jvm_signal_installing) {
73 if (tid != pthread_self()) {
74 pthread_cond_wait(&cond, &mutex);
75 }
76 }
77 }
78
79 static void signal_unlock() {
80 pthread_mutex_unlock(&mutex);
81 }
82
83 static sa_handler_t call_os_signal(int sig, sa_handler_t disp,
84 bool is_sigset) {
85 if (os_signal == NULL) {
86 if (!is_sigset) {
87 os_signal = (signal_t)dlsym(RTLD_NEXT, "signal");
88 } else {
89 os_signal = (signal_t)dlsym(RTLD_NEXT, "sigset");
90 }
91 if (os_signal == NULL) {
92 printf("%s\n", dlerror());
93 exit(0);
94 }
95 }
96 return (*os_signal)(sig, disp);
97 }
98
99 static void save_signal_handler(int sig, sa_handler_t disp) {
100 sigset_t set;
101 sact[sig].sa_handler = disp;
102 sigemptyset(&set);
103 sact[sig].sa_mask = set;
104 sact[sig].sa_flags = 0;
105 }
106
107 static sa_handler_t set_signal(int sig, sa_handler_t disp, bool is_sigset) {
108 sa_handler_t oldhandler;
109 bool sigused;
110
111 signal_lock();
112
113 sigused = (sig < NSIG) && ((MASK(sig) & jvmsigs) != 0);
114 if (jvm_signal_installed && sigused) {
115 /* jvm has installed its signal handler for this signal. */
116 /* Save the handler. Don't really install it. */
117 oldhandler = sact[sig].sa_handler;
118 save_signal_handler(sig, disp);
119
120 signal_unlock();
121 return oldhandler;
122 } else if (sig < NSIG && jvm_signal_installing) {
123 /* jvm is installing its signal handlers. Install the new
124 * handlers and save the old ones. jvm uses sigaction().
125 * Leave the piece here just in case. */
126 oldhandler = call_os_signal(sig, disp, is_sigset);
127 save_signal_handler(sig, oldhandler);
128
129 /* Record the signals used by jvm */
130 jvmsigs |= MASK(sig);
131
132 signal_unlock();
133 return oldhandler;
134 } else {
135 /* jvm has no relation with this signal (yet). Install the
136 * the handler. */
137 oldhandler = call_os_signal(sig, disp, is_sigset);
138
139 signal_unlock();
140 return oldhandler;
141 }
142 }
143
144 sa_handler_t signal(int sig, sa_handler_t disp) {
145 return set_signal(sig, disp, false);
146 }
147
148 sa_handler_t sigset(int sig, sa_handler_t disp) {
149 return set_signal(sig, disp, true);
150 }
151
152 static int call_os_sigaction(int sig, const struct sigaction *act,
153 struct sigaction *oact) {
154 if (os_sigaction == NULL) {
155 os_sigaction = (sigaction_t)dlsym(RTLD_NEXT, "sigaction");
156 if (os_sigaction == NULL) {
157 printf("%s\n", dlerror());
158 exit(0);
159 }
160 }
161 return (*os_sigaction)(sig, act, oact);
162 }
163
164 int sigaction(int sig, const struct sigaction *act, struct sigaction *oact) {
165 int res;
166 bool sigused;
167 struct sigaction oldAct;
168
169 signal_lock();
170
171 sigused = (sig < NSIG) && ((MASK(sig) & jvmsigs) != 0);
172 if (jvm_signal_installed && sigused) {
173 /* jvm has installed its signal handler for this signal. */
174 /* Save the handler. Don't really install it. */
175 if (oact != NULL) {
176 *oact = sact[sig];
177 }
178 if (act != NULL) {
179 sact[sig] = *act;
180 }
181
182 signal_unlock();
183 return 0;
184 } else if (sig < NSIG && jvm_signal_installing) {
185 /* jvm is installing its signal handlers. Install the new
186 * handlers and save the old ones. */
187 res = call_os_sigaction(sig, act, &oldAct);
188 sact[sig] = oldAct;
189 if (oact != NULL) {
190 *oact = oldAct;
191 }
192
193 /* Record the signals used by jvm */
194 jvmsigs |= MASK(sig);
195
196 signal_unlock();
197 return res;
198 } else {
199 /* jvm has no relation with this signal (yet). Install the
200 * the handler. */
201 res = call_os_sigaction(sig, act, oact);
202
203 signal_unlock();
204 return res;
205 }
206 }
207
208 /* The three functions for the jvm to call into */
209 void JVM_begin_signal_setting() {
210 signal_lock();
211 jvm_signal_installing = true;
212 tid = pthread_self();
213 signal_unlock();
214 }
215
216 void JVM_end_signal_setting() {
217 signal_lock();
218 jvm_signal_installed = true;
219 jvm_signal_installing = false;
220 pthread_cond_broadcast(&cond);
221 signal_unlock();
222 }
223
224 struct sigaction *JVM_get_signal_action(int sig) {
225 /* Does race condition make sense here? */
226 if ((MASK(sig) & jvmsigs) != 0) {
227 return &sact[sig];
228 }
229 return NULL;
230 }