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
49static struct sigaction sact[NSIG]; /* saved signal handlers */
50static uint64_t jvmsigs = 0; /* signals used by jvm */
51
52/* used to synchronize the installation of signal handlers */
53static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
54static pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
55static pthread_t tid = 0;
56
57typedef void (*sa_handler_t)(int);
58typedef void (*sa_sigaction_t)(int, siginfo_t *, void *);
59typedef sa_handler_t (*signal_t)(int, sa_handler_t);
60typedef int (*sigaction_t)(int, const struct sigaction *, struct sigaction *);
61
62static signal_t os_signal = 0; /* os's version of signal()/sigset() */
63static sigaction_t os_sigaction = 0; /* os's version of sigaction() */
64
65static bool jvm_signal_installing = false;
66static bool jvm_signal_installed = false;
67
68static 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
79static void signal_unlock() {
80  pthread_mutex_unlock(&mutex);
81}
82
83static 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
99static 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
107static 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
144sa_handler_t signal(int sig, sa_handler_t disp) {
145  return set_signal(sig, disp, false);
146}
147
148sa_handler_t sigset(int sig, sa_handler_t disp) {
149  return set_signal(sig, disp, true);
150 }
151
152static 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
164int 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 */
209void JVM_begin_signal_setting() {
210  signal_lock();
211  jvm_signal_installing = true;
212  tid = pthread_self();
213  signal_unlock();
214}
215
216void 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
224struct 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}
231