1 /*
   2  * Copyright (c) 2001, 2015, 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 #include <stdint.h>
  40 
  41 #define MASK(sig) ((uint32_t)1 << (sig-1))  // 0 is not a signal.
  42 #if (32 < NSIG-1)
  43 #error "Not all signals can be encoded in jvmsigs. Adapt its type!"
  44 #endif
  45 static struct sigaction sact[NSIG]; /* saved signal handlers */
  46 static uint32_t jvmsigs = 0; /* signals used by jvm */
  47 static __thread bool reentry = false; /* prevent reentry deadlock (per-thread) */
  48 
  49 /* used to synchronize the installation of signal handlers */
  50 static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
  51 static pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
  52 static pthread_t tid = 0;
  53 
  54 typedef void (*sa_handler_t)(int);
  55 typedef void (*sa_sigaction_t)(int, siginfo_t *, void *);
  56 typedef sa_handler_t (*signal_t)(int, sa_handler_t);
  57 typedef int (*sigaction_t)(int, const struct sigaction *, struct sigaction *);
  58 
  59 static signal_t os_signal = 0; /* os's version of signal()/sigset() */
  60 static sigaction_t os_sigaction = 0; /* os's version of sigaction() */
  61 
  62 static bool jvm_signal_installing = false;
  63 static bool jvm_signal_installed = false;
  64 
  65 static void signal_lock() {
  66   pthread_mutex_lock(&mutex);
  67   /* When the jvm is installing its set of signal handlers, threads
  68    * other than the jvm thread should wait */
  69   if (jvm_signal_installing) {
  70     if (tid != pthread_self()) {
  71       pthread_cond_wait(&cond, &mutex);
  72     }
  73   }
  74 }
  75 
  76 static void signal_unlock() {
  77   pthread_mutex_unlock(&mutex);
  78 }
  79 
  80 static sa_handler_t call_os_signal(int sig, sa_handler_t disp,
  81                                    bool is_sigset) {
  82   sa_handler_t res;
  83 
  84   if (os_signal == NULL) {
  85     if (!is_sigset) {
  86       os_signal = (signal_t)dlsym(RTLD_NEXT, "signal");
  87     } else {
  88       os_signal = (signal_t)dlsym(RTLD_NEXT, "sigset");
  89     }
  90     if (os_signal == NULL) {
  91       printf("%s\n", dlerror());
  92       exit(0);
  93     }
  94   }
  95   reentry = true;
  96   res = (*os_signal)(sig, disp);
  97   reentry = false;
  98   return res;
  99 }
 100 
 101 static void save_signal_handler(int sig, sa_handler_t disp) {
 102   sigset_t set;
 103   sact[sig].sa_handler = disp;
 104   sigemptyset(&set);
 105   sact[sig].sa_mask = set;
 106   sact[sig].sa_flags = 0;
 107 }
 108 
 109 static sa_handler_t set_signal(int sig, sa_handler_t disp, bool is_sigset) {
 110   sa_handler_t oldhandler;
 111   bool sigused;
 112 
 113   signal_lock();
 114 
 115   sigused = (MASK(sig) & jvmsigs) != 0;
 116   if (jvm_signal_installed && sigused) {
 117     /* jvm has installed its signal handler for this signal. */
 118     /* Save the handler. Don't really install it. */
 119     oldhandler = sact[sig].sa_handler;
 120     save_signal_handler(sig, disp);
 121 
 122     signal_unlock();
 123     return oldhandler;
 124   } else if (jvm_signal_installing) {
 125     /* jvm is installing its signal handlers. Install the new
 126      * handlers and save the old ones. jvm uses sigaction().
 127      * Leave the piece here just in case. */
 128     oldhandler = call_os_signal(sig, disp, is_sigset);
 129     save_signal_handler(sig, oldhandler);
 130 
 131     /* Record the signals used by jvm */
 132     jvmsigs |= MASK(sig);
 133 
 134     signal_unlock();
 135     return oldhandler;
 136   } else {
 137     /* jvm has no relation with this signal (yet). Install the
 138      * the handler. */
 139     oldhandler = call_os_signal(sig, disp, is_sigset);
 140 
 141     signal_unlock();
 142     return oldhandler;
 143   }
 144 }
 145 
 146 sa_handler_t signal(int sig, sa_handler_t disp) {
 147   return set_signal(sig, disp, false);
 148 }
 149 
 150 sa_handler_t sigset(int sig, sa_handler_t disp) {
 151   printf("sigset() is not supported by BSD");
 152   exit(0);
 153  }
 154 
 155 static int call_os_sigaction(int sig, const struct sigaction  *act,
 156                              struct sigaction *oact) {
 157   if (os_sigaction == NULL) {
 158     os_sigaction = (sigaction_t)dlsym(RTLD_NEXT, "sigaction");
 159     if (os_sigaction == NULL) {
 160       printf("%s\n", dlerror());
 161       exit(0);
 162     }
 163   }
 164   return (*os_sigaction)(sig, act, oact);
 165 }
 166 
 167 int sigaction(int sig, const struct sigaction *act, struct sigaction *oact) {
 168   int res;
 169   bool sigused;
 170   struct sigaction oldAct;
 171 
 172   if (reentry) {
 173     return call_os_sigaction(sig, act, oact);
 174   }
 175 
 176   signal_lock();
 177 
 178   sigused = (MASK(sig) & jvmsigs) != 0;
 179   if (jvm_signal_installed && sigused) {
 180     /* jvm has installed its signal handler for this signal. */
 181     /* Save the handler. Don't really install it. */
 182     if (oact != NULL) {
 183       *oact = sact[sig];
 184     }
 185     if (act != NULL) {
 186       sact[sig] = *act;
 187     }
 188 
 189     signal_unlock();
 190     return 0;
 191   } else if (jvm_signal_installing) {
 192     /* jvm is installing its signal handlers. Install the new
 193      * handlers and save the old ones. */
 194     res = call_os_sigaction(sig, act, &oldAct);
 195     sact[sig] = oldAct;
 196     if (oact != NULL) {
 197       *oact = oldAct;
 198     }
 199 
 200     /* Record the signals used by jvm */
 201     jvmsigs |= MASK(sig);
 202 
 203     signal_unlock();
 204     return res;
 205   } else {
 206     /* jvm has no relation with this signal (yet). Install the
 207      * the handler. */
 208     res = call_os_sigaction(sig, act, oact);
 209 
 210     signal_unlock();
 211     return res;
 212   }
 213 }
 214 
 215 /* The three functions for the jvm to call into */
 216 void JVM_begin_signal_setting() {
 217   signal_lock();
 218   jvm_signal_installing = true;
 219   tid = pthread_self();
 220   signal_unlock();
 221 }
 222 
 223 void JVM_end_signal_setting() {
 224   signal_lock();
 225   jvm_signal_installed = true;
 226   jvm_signal_installing = false;
 227   pthread_cond_broadcast(&cond);
 228   signal_unlock();
 229 }
 230 
 231 struct sigaction *JVM_get_signal_action(int sig) {
 232   /* Does race condition make sense here? */
 233   if ((MASK(sig) & jvmsigs) != 0) {
 234     return &sact[sig];
 235   }
 236   return NULL;
 237 }