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 }