lib/fatal-signal.c

   1 /* Emergency actions in case of a fatal signal.
   2    Copyright (C) 2003-2004, 2006-2018 Free Software Foundation, Inc.
   3    Written by Bruno Haible <bruno@clisp.org>, 2003.
   4
   5    This program is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  17
  18
  19 #include <config.h>
  20
  21 /* Specification.  */
  22 #include "fatal-signal.h"
  23
  24 #include <stdbool.h>
  25 #include <stdlib.h>
  26 #include <signal.h>
  27 #include <unistd.h>
  28
  29 #include "sig-handler.h"
  30 #include "xalloc.h"
  31
  32 #define SIZEOF(a) (sizeof(a) / sizeof(a[0]))
  33
  34 /* ========================================================================= */
  35
  36
  37 /* The list of fatal signals.
  38    These are those signals whose default action is to terminate the process
  39    without a core dump, except
  40      SIGKILL - because it cannot be caught,
  41      SIGALRM SIGUSR1 SIGUSR2 SIGPOLL SIGIO SIGLOST - because applications
  42        often use them for their own purpose,
  43      SIGPROF SIGVTALRM - because they are used for profiling,
  44      SIGSTKFLT - because it is more similar to SIGFPE, SIGSEGV, SIGBUS,
  45      SIGSYS - because it is more similar to SIGABRT, SIGSEGV,
  46      SIGPWR - because it of too special use,
  47      SIGRTMIN...SIGRTMAX - because they are reserved for application use.
  48    plus
  49      SIGXCPU, SIGXFSZ - because they are quite similar to SIGTERM.  */
  50
  51 static int fatal_signals[] =
  52   {
  53     /* ISO C 99 signals.  */
  54 #ifdef SIGINT
  55     SIGINT,
  56 #endif
  57 #ifdef SIGTERM
  58     SIGTERM,
  59 #endif
  60     /* POSIX:2001 signals.  */
  61 #ifdef SIGHUP
  62     SIGHUP,
  63 #endif
  64 #ifdef SIGPIPE
  65     SIGPIPE,
  66 #endif
  67     /* BSD signals.  */
  68 #ifdef SIGXCPU
  69     SIGXCPU,
  70 #endif
  71 #ifdef SIGXFSZ
  72     SIGXFSZ,
  73 #endif
  74     /* Native Windows signals.  */
  75 #ifdef SIGBREAK
  76     SIGBREAK,
  77 #endif
  78     0
  79   };
  80
  81 #define num_fatal_signals (SIZEOF (fatal_signals) - 1)
  82
  83 /* Eliminate signals whose signal handler is SIG_IGN.  */
  84
  85 static void
  86 init_fatal_signals (void)
  87 {
  88   static bool fatal_signals_initialized = false;
  89   if (!fatal_signals_initialized)
  90     {
  91       size_t i;
  92
  93       for (i = 0; i < num_fatal_signals; i++)
  94         {
  95           struct sigaction action;
  96
  97           if (sigaction (fatal_signals[i], NULL, &action) >= 0
  98               && get_handler (&action) == SIG_IGN)
  99             fatal_signals[i] = -1;
 100         }
 101
 102       fatal_signals_initialized = true;
 103     }
 104 }
 105
 106
 107 /* ========================================================================= */
 108
 109
 110 typedef void (*action_t) (void);
 111
 112 /* Type of an entry in the actions array.
 113    The 'action' field is accessed from within the fatal_signal_handler(),
 114    therefore we mark it as 'volatile'.  */
 115 typedef struct
 116 {
 117   volatile action_t action;
 118 }
 119 actions_entry_t;
 120
 121 /* The registered cleanup actions.  */
 122 static actions_entry_t static_actions[32];
 123 static actions_entry_t * volatile actions = static_actions;
 124 static sig_atomic_t volatile actions_count = 0;
 125 static size_t actions_allocated = SIZEOF (static_actions);
 126
 127
 128 /* The saved signal handlers.
 129    Size 32 would not be sufficient: On HP-UX, SIGXCPU = 33, SIGXFSZ = 34.  */
 130 static struct sigaction saved_sigactions[64];
 131
 132
 133 /* Uninstall the handlers.  */
 134 static void
 135 uninstall_handlers (void)
 136 {
 137   size_t i;
 138
 139   for (i = 0; i < num_fatal_signals; i++)
 140     if (fatal_signals[i] >= 0)
 141       {
 142         int sig = fatal_signals[i];
 143         if (saved_sigactions[sig].sa_handler == SIG_IGN)
 144           saved_sigactions[sig].sa_handler = SIG_DFL;
 145         sigaction (sig, &saved_sigactions[sig], NULL);
 146       }
 147 }
 148
 149
 150 /* The signal handler.  It gets called asynchronously.  */
 151 static void
 152 fatal_signal_handler (int sig)
 153 {
 154   for (;;)
 155     {
 156       /* Get the last registered cleanup action, in a reentrant way.  */
 157       action_t action;
 158       size_t n = actions_count;
 159       if (n == 0)
 160         break;
 161       n--;
 162       actions_count = n;
 163       action = actions[n].action;
 164       /* Execute the action.  */
 165       action ();
 166     }
 167
 168   /* Now execute the signal's default action.
 169      If the signal being delivered was blocked, the re-raised signal would be
 170      delivered when this handler returns.  But the way we install this handler,
 171      no signal is blocked, and the re-raised signal is delivered already
 172      during raise().  */
 173   uninstall_handlers ();
 174   raise (sig);
 175 }
 176
 177
 178 /* Install the handlers.  */
 179 static void
 180 install_handlers (void)
 181 {
 182   size_t i;
 183   struct sigaction action;
 184
 185   action.sa_handler = &fatal_signal_handler;
 186   /* If we get a fatal signal while executing fatal_signal_handler, enter
 187      fatal_signal_handler recursively, since it is reentrant.  Hence no
 188      SA_RESETHAND.  */
 189   action.sa_flags = SA_NODEFER;
 190   sigemptyset (&action.sa_mask);
 191   for (i = 0; i < num_fatal_signals; i++)
 192     if (fatal_signals[i] >= 0)
 193       {
 194         int sig = fatal_signals[i];
 195
 196         if (!(sig < sizeof (saved_sigactions) / sizeof (saved_sigactions[0])))
 197           abort ();
 198         sigaction (sig, &action, &saved_sigactions[sig]);
 199       }
 200 }
 201
 202
 203 /* Register a cleanup function to be executed when a catchable fatal signal
 204    occurs.  */
 205 void
 206 at_fatal_signal (action_t action)
 207 {
 208   static bool cleanup_initialized = false;
 209   if (!cleanup_initialized)
 210     {
 211       init_fatal_signals ();
 212       install_handlers ();
 213       cleanup_initialized = true;
 214     }
 215
 216   if (actions_count == actions_allocated)
 217     {
 218       /* Extend the actions array.  Note that we cannot use xrealloc(),
 219          because then the cleanup() function could access an already
 220          deallocated array.  */
 221       actions_entry_t *old_actions = actions;
 222       size_t old_actions_allocated = actions_allocated;
 223       size_t new_actions_allocated = 2 * actions_allocated;
 224       actions_entry_t *new_actions =
 225         XNMALLOC (new_actions_allocated, actions_entry_t);
 226       size_t k;
 227
 228       /* Don't use memcpy() here, because memcpy takes non-volatile arguments
 229          and is therefore not guaranteed to complete all memory stores before
 230          the next statement.  */
 231       for (k = 0; k < old_actions_allocated; k++)
 232         new_actions[k] = old_actions[k];
 233       actions = new_actions;
 234       actions_allocated = new_actions_allocated;
 235       /* Now we can free the old actions array.  */
 236       if (old_actions != static_actions)
 237         free (old_actions);
 238     }
 239   /* The two uses of 'volatile' in the types above (and ISO C 99 section
 240      5.1.2.3.(5)) ensure that we increment the actions_count only after
 241      the new action has been written to the memory location
 242      actions[actions_count].  */
 243   actions[actions_count].action = action;
 244   actions_count++;
 245 }
 246
 247
 248 /* ========================================================================= */
 249
 250
 251 static sigset_t fatal_signal_set;
 252
 253 static void
 254 init_fatal_signal_set (void)
 255 {
 256   static bool fatal_signal_set_initialized = false;
 257   if (!fatal_signal_set_initialized)
 258     {
 259       size_t i;
 260
 261       init_fatal_signals ();
 262
 263       sigemptyset (&fatal_signal_set);
 264       for (i = 0; i < num_fatal_signals; i++)
 265         if (fatal_signals[i] >= 0)
 266           sigaddset (&fatal_signal_set, fatal_signals[i]);
 267
 268       fatal_signal_set_initialized = true;
 269     }
 270 }
 271
 272 /* Temporarily delay the catchable fatal signals.  */
 273 void
 274 block_fatal_signals (void)
 275 {
 276   init_fatal_signal_set ();
 277   sigprocmask (SIG_BLOCK, &fatal_signal_set, NULL);
 278 }
 279
 280 /* Stop delaying the catchable fatal signals.  */
 281 void
 282 unblock_fatal_signals (void)
 283 {
 284   init_fatal_signal_set ();
 285   sigprocmask (SIG_UNBLOCK, &fatal_signal_set, NULL);
 286 }