lib/fatal-signal.c

   1 /* Emergency actions in case of a fatal signal.
   2    Copyright (C) 2003-2004, 2006-2024 Free Software Foundation, Inc.
   3    Written by Bruno Haible <bruno@clisp.org>, 2003.
   4
   5    This file is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU Lesser General Public License as
   7    published by the Free Software Foundation; either version 2.1 of the
   8    License, or (at your option) any later version.
   9
  10    This file 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 Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser 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 <stdlib.h>
  25 #include <signal.h>
  26 #include <unistd.h>
  27
  28 #include "glthread/lock.h"
  29 #include "glthread/once.h"
  30 #include "thread-optim.h"
  31 #include "sig-handler.h"
  32
  33 #define SIZEOF(a) (sizeof(a) / sizeof(a[0]))
  34
  35 /* ========================================================================= */
  36
  37
  38 /* The list of fatal signals.
  39    These are those signals whose default action is to terminate the process
  40    without a core dump, except
  41      SIGKILL - because it cannot be caught,
  42      SIGALRM SIGUSR1 SIGUSR2 SIGPOLL SIGIO SIGLOST - because applications
  43        often use them for their own purpose,
  44      SIGPROF SIGVTALRM - because they are used for profiling,
  45      SIGSTKFLT - because it is more similar to SIGFPE, SIGSEGV, SIGBUS,
  46      SIGSYS - because it is more similar to SIGABRT, SIGSEGV,
  47      SIGPWR - because it of too special use,
  48      SIGRTMIN...SIGRTMAX - because they are reserved for application use.
  49    plus
  50      SIGXCPU, SIGXFSZ - because they are quite similar to SIGTERM.  */
  51
  52 static int fatal_signals[] =
  53   {
  54     /* ISO C 99 signals.  */
  55 #ifdef SIGINT
  56     SIGINT,
  57 #endif
  58 #ifdef SIGTERM
  59     SIGTERM,
  60 #endif
  61     /* POSIX:2001 signals.  */
  62 #ifdef SIGHUP
  63     SIGHUP,
  64 #endif
  65 #ifdef SIGPIPE
  66     SIGPIPE,
  67 #endif
  68     /* BSD signals.  */
  69 #ifdef SIGXCPU
  70     SIGXCPU,
  71 #endif
  72 #ifdef SIGXFSZ
  73     SIGXFSZ,
  74 #endif
  75     /* Native Windows signals.  */
  76 #ifdef SIGBREAK
  77     SIGBREAK,
  78 #endif
  79     0
  80   };
  81
  82 #define num_fatal_signals (SIZEOF (fatal_signals) - 1)
  83
  84 /* Eliminate signals whose signal handler is SIG_IGN.  */
  85
  86 static void
  87 init_fatal_signals (void)
  88 {
  89   /* This function is multithread-safe even without synchronization, because
  90      if two threads execute it simultaneously, the fatal_signals[] array will
  91      not change any more after the first of the threads has completed this
  92      function.  */
  93   static bool fatal_signals_initialized = false;
  94   if (!fatal_signals_initialized)
  95     {
  96       size_t i;
  97
  98       for (i = 0; i < num_fatal_signals; i++)
  99         {
 100           struct sigaction action;
 101
 102           if (sigaction (fatal_signals[i], NULL, &action) >= 0
 103               && get_handler (&action) == SIG_IGN)
 104             fatal_signals[i] = -1;
 105         }
 106
 107       fatal_signals_initialized = true;
 108     }
 109 }
 110
 111
 112 /* ========================================================================= */
 113
 114
 115 typedef _GL_ASYNC_SAFE void (*action_t) (int sig);
 116
 117 /* Type of an entry in the actions array.
 118    The 'action' field is accessed from within the fatal_signal_handler(),
 119    therefore we mark it as 'volatile'.  */
 120 typedef struct
 121 {
 122   volatile action_t action;
 123 }
 124 actions_entry_t;
 125
 126 /* The registered cleanup actions.  */
 127 static actions_entry_t static_actions[32];
 128 static actions_entry_t * volatile actions = static_actions;
 129 static sig_atomic_t volatile actions_count = 0;
 130 static size_t actions_allocated = SIZEOF (static_actions);
 131
 132
 133 /* The saved signal handlers.
 134    Size 32 would not be sufficient: On HP-UX, SIGXCPU = 33, SIGXFSZ = 34.  */
 135 static struct sigaction saved_sigactions[64];
 136
 137
 138 /* Uninstall the handlers.  */
 139 static _GL_ASYNC_SAFE void
 140 uninstall_handlers (void)
 141 {
 142   size_t i;
 143
 144   for (i = 0; i < num_fatal_signals; i++)
 145     if (fatal_signals[i] >= 0)
 146       {
 147         int sig = fatal_signals[i];
 148         if (saved_sigactions[sig].sa_handler == SIG_IGN)
 149           saved_sigactions[sig].sa_handler = SIG_DFL;
 150         sigaction (sig, &saved_sigactions[sig], NULL);
 151       }
 152 }
 153
 154
 155 /* The signal handler.  It gets called asynchronously.  */
 156 static _GL_ASYNC_SAFE void
 157 fatal_signal_handler (int sig)
 158 {
 159   for (;;)
 160     {
 161       /* Get the last registered cleanup action, in a reentrant way.  */
 162       action_t action;
 163       size_t n = actions_count;
 164       if (n == 0)
 165         break;
 166       n--;
 167       actions_count = n;
 168       action = actions[n].action;
 169       /* Execute the action.  */
 170       action (sig);
 171     }
 172
 173   /* Now execute the signal's default action.
 174      If the signal being delivered was blocked, the re-raised signal would be
 175      delivered when this handler returns.  But the way we install this handler,
 176      no signal is blocked, and the re-raised signal is delivered already
 177      during raise().  */
 178   uninstall_handlers ();
 179   raise (sig);
 180 }
 181
 182
 183 /* Install the handlers.  */
 184 static void
 185 install_handlers (void)
 186 {
 187   size_t i;
 188   struct sigaction action;
 189
 190   action.sa_handler = &fatal_signal_handler;
 191   /* If we get a fatal signal while executing fatal_signal_handler, enter
 192      fatal_signal_handler recursively, since it is reentrant.  Hence no
 193      SA_RESETHAND.  */
 194   action.sa_flags = SA_NODEFER;
 195   sigemptyset (&action.sa_mask);
 196   for (i = 0; i < num_fatal_signals; i++)
 197     if (fatal_signals[i] >= 0)
 198       {
 199         int sig = fatal_signals[i];
 200
 201         if (!(sig < sizeof (saved_sigactions) / sizeof (saved_sigactions[0])))
 202           abort ();
 203         sigaction (sig, &action, &saved_sigactions[sig]);
 204       }
 205 }
 206
 207
 208 /* Lock that makes at_fatal_signal multi-thread safe.  */
 209 gl_lock_define_initialized (static, at_fatal_signal_lock)
 210
 211 /* Register a cleanup function to be executed when a catchable fatal signal
 212    occurs.  */
 213 int
 214 at_fatal_signal (action_t action)
 215 {
 216   bool mt = gl_multithreaded ();
 217
 218   if (mt) gl_lock_lock (at_fatal_signal_lock);
 219
 220   static bool cleanup_initialized = false;
 221   if (!cleanup_initialized)
 222     {
 223       init_fatal_signals ();
 224       install_handlers ();
 225       cleanup_initialized = true;
 226     }
 227
 228   int ret = 0;
 229
 230   if (actions_count == actions_allocated)
 231     {
 232       /* Extend the actions array.  Note that we cannot use xrealloc(),
 233          because then the cleanup() function could access an already
 234          deallocated array.  */
 235       actions_entry_t *old_actions = actions;
 236       size_t old_actions_allocated = actions_allocated;
 237       size_t new_actions_allocated = 2 * actions_allocated;
 238       actions_entry_t *new_actions =
 239         (actions_entry_t *)
 240         malloc (new_actions_allocated * sizeof (actions_entry_t));
 241       if (new_actions == NULL)
 242         {
 243           ret = -1;
 244           goto done;
 245         }
 246
 247       size_t k;
 248       /* Don't use memcpy() here, because memcpy takes non-volatile arguments
 249          and is therefore not guaranteed to complete all memory stores before
 250          the next statement.  */
 251       for (k = 0; k < old_actions_allocated; k++)
 252         new_actions[k] = old_actions[k];
 253       actions = new_actions;
 254       actions_allocated = new_actions_allocated;
 255       /* Now we can free the old actions array.  */
 256       /* No, we can't do that.  If fatal_signal_handler is running in a
 257          different thread and has already fetched the actions pointer (getting
 258          old_actions) but not yet accessed its n-th element, that thread may
 259          crash when accessing an element of the already freed old_actions
 260          array.  */
 261       #if 0
 262       if (old_actions != static_actions)
 263         free (old_actions);
 264       #endif
 265     }
 266   /* The two uses of 'volatile' in the types above (and ISO C 99 section
 267      5.1.2.3.(5)) ensure that we increment the actions_count only after
 268      the new action has been written to the memory location
 269      actions[actions_count].  */
 270   actions[actions_count].action = action;
 271   actions_count++;
 272
 273  done:
 274   if (mt) gl_lock_unlock (at_fatal_signal_lock);
 275
 276   return ret;
 277 }
 278
 279
 280 /* ========================================================================= */
 281
 282
 283 static sigset_t fatal_signal_set;
 284
 285 static void
 286 do_init_fatal_signal_set (void)
 287 {
 288   size_t i;
 289
 290   init_fatal_signals ();
 291
 292   sigemptyset (&fatal_signal_set);
 293   for (i = 0; i < num_fatal_signals; i++)
 294     if (fatal_signals[i] >= 0)
 295       sigaddset (&fatal_signal_set, fatal_signals[i]);
 296 }
 297
 298 /* Ensure that do_init_fatal_signal_set is called once only.  */
 299 gl_once_define(static, fatal_signal_set_once)
 300
 301 static void
 302 init_fatal_signal_set (void)
 303 {
 304   gl_once (fatal_signal_set_once, do_init_fatal_signal_set);
 305 }
 306
 307 /* Lock and counter that allow block_fatal_signals/unblock_fatal_signals pairs
 308    to occur in different threads and even overlap in time.  */
 309 gl_lock_define_initialized (static, fatal_signals_block_lock)
 310 static unsigned int fatal_signals_block_counter = 0;
 311
 312 /* Temporarily delay the catchable fatal signals.  */
 313 void
 314 block_fatal_signals (void)
 315 {
 316   bool mt = gl_multithreaded ();
 317
 318   if (mt) gl_lock_lock (fatal_signals_block_lock);
 319
 320   if (fatal_signals_block_counter++ == 0)
 321     {
 322       init_fatal_signal_set ();
 323       sigprocmask (SIG_BLOCK, &fatal_signal_set, NULL);
 324     }
 325
 326   if (mt) gl_lock_unlock (fatal_signals_block_lock);
 327 }
 328
 329 /* Stop delaying the catchable fatal signals.  */
 330 void
 331 unblock_fatal_signals (void)
 332 {
 333   bool mt = gl_multithreaded ();
 334
 335   if (mt) gl_lock_lock (fatal_signals_block_lock);
 336
 337   if (fatal_signals_block_counter == 0)
 338     /* There are more calls to unblock_fatal_signals() than to
 339        block_fatal_signals().  */
 340     abort ();
 341   if (--fatal_signals_block_counter == 0)
 342     {
 343       init_fatal_signal_set ();
 344       sigprocmask (SIG_UNBLOCK, &fatal_signal_set, NULL);
 345     }
 346
 347   if (mt) gl_lock_unlock (fatal_signals_block_lock);
 348 }
 349
 350
 351 unsigned int
 352 get_fatal_signals (int signals[64])
 353 {
 354   init_fatal_signal_set ();
 355
 356   {
 357     int *p = signals;
 358     size_t i;
 359
 360     for (i = 0; i < num_fatal_signals; i++)
 361       if (fatal_signals[i] >= 0)
 362         *p++ = fatal_signals[i];
 363     return p - signals;
 364   }
 365 }
 366
 367 const sigset_t *
 368 get_fatal_signal_set (void)
 369 {
 370   init_fatal_signal_set ();
 371   return &fatal_signal_set;
 372 }