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/* Emergency actions in case of a fatal signal.
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Copyright (C) 2003-2004, 2006-2012 Free Software Foundation, Inc.
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Written by Bruno Haible <bruno@clisp.org>, 2003.
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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#include "fatal-signal.h"
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#include "sig-handler.h"
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#define SIZEOF(a) (sizeof(a) / sizeof(a[0]))
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/* ========================================================================= */
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/* The list of fatal signals.
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These are those signals whose default action is to terminate the process
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without a core dump, except
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SIGKILL - because it cannot be caught,
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SIGALRM SIGUSR1 SIGUSR2 SIGPOLL SIGIO SIGLOST - because applications
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often use them for their own purpose,
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SIGPROF SIGVTALRM - because they are used for profiling,
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SIGSTKFLT - because it is more similar to SIGFPE, SIGSEGV, SIGBUS,
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SIGSYS - because it is more similar to SIGABRT, SIGSEGV,
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SIGPWR - because it of too special use,
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SIGRTMIN...SIGRTMAX - because they are reserved for application use.
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SIGXCPU, SIGXFSZ - because they are quite similar to SIGTERM. */
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static int fatal_signals[] =
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/* ISO C 99 signals. */
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/* POSIX:2001 signals. */
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/* Native Windows signals. */
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#define num_fatal_signals (SIZEOF (fatal_signals) - 1)
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/* Eliminate signals whose signal handler is SIG_IGN. */
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init_fatal_signals (void)
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static bool fatal_signals_initialized = false;
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if (!fatal_signals_initialized)
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for (i = 0; i < num_fatal_signals; i++)
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struct sigaction action;
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if (sigaction (fatal_signals[i], NULL, &action) >= 0
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&& get_handler (&action) == SIG_IGN)
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fatal_signals[i] = -1;
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fatal_signals_initialized = true;
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/* ========================================================================= */
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typedef void (*action_t) (void);
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/* Type of an entry in the actions array.
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The 'action' field is accessed from within the fatal_signal_handler(),
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therefore we mark it as 'volatile'. */
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volatile action_t action;
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/* The registered cleanup actions. */
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static actions_entry_t static_actions[32];
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static actions_entry_t * volatile actions = static_actions;
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static sig_atomic_t volatile actions_count = 0;
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static size_t actions_allocated = SIZEOF (static_actions);
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/* The saved signal handlers.
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Size 32 would not be sufficient: On HP-UX, SIGXCPU = 33, SIGXFSZ = 34. */
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static struct sigaction saved_sigactions[64];
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/* Uninstall the handlers. */
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uninstall_handlers (void)
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for (i = 0; i < num_fatal_signals; i++)
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if (fatal_signals[i] >= 0)
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int sig = fatal_signals[i];
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if (saved_sigactions[sig].sa_handler == SIG_IGN)
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saved_sigactions[sig].sa_handler = SIG_DFL;
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sigaction (sig, &saved_sigactions[sig], NULL);
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/* The signal handler. It gets called asynchronously. */
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fatal_signal_handler (int sig)
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/* Get the last registered cleanup action, in a reentrant way. */
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size_t n = actions_count;
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action = actions[n].action;
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/* Execute the action. */
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/* Now execute the signal's default action.
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If the signal being delivered was blocked, the re-raised signal would be
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delivered when this handler returns. But the way we install this handler,
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no signal is blocked, and the re-raised signal is delivered already
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uninstall_handlers ();
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/* Install the handlers. */
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install_handlers (void)
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struct sigaction action;
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action.sa_handler = &fatal_signal_handler;
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/* If we get a fatal signal while executing fatal_signal_handler, enter
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fatal_signal_handler recursively, since it is reentrant. Hence no
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action.sa_flags = SA_NODEFER;
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sigemptyset (&action.sa_mask);
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for (i = 0; i < num_fatal_signals; i++)
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if (fatal_signals[i] >= 0)
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int sig = fatal_signals[i];
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if (!(sig < sizeof (saved_sigactions) / sizeof (saved_sigactions[0])))
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sigaction (sig, &action, &saved_sigactions[sig]);
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/* Register a cleanup function to be executed when a catchable fatal signal
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at_fatal_signal (action_t action)
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static bool cleanup_initialized = false;
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if (!cleanup_initialized)
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init_fatal_signals ();
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cleanup_initialized = true;
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if (actions_count == actions_allocated)
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/* Extend the actions array. Note that we cannot use xrealloc(),
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because then the cleanup() function could access an already
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deallocated array. */
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actions_entry_t *old_actions = actions;
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size_t old_actions_allocated = actions_allocated;
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size_t new_actions_allocated = 2 * actions_allocated;
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actions_entry_t *new_actions =
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XNMALLOC (new_actions_allocated, actions_entry_t);
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/* Don't use memcpy() here, because memcpy takes non-volatile arguments
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and is therefore not guaranteed to complete all memory stores before
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the next statement. */
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for (k = 0; k < old_actions_allocated; k++)
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new_actions[k] = old_actions[k];
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actions = new_actions;
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actions_allocated = new_actions_allocated;
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/* Now we can free the old actions array. */
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if (old_actions != static_actions)
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/* The two uses of 'volatile' in the types above (and ISO C 99 section
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5.1.2.3.(5)) ensure that we increment the actions_count only after
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the new action has been written to the memory location
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actions[actions_count]. */
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actions[actions_count].action = action;
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/* ========================================================================= */
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static sigset_t fatal_signal_set;
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init_fatal_signal_set (void)
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static bool fatal_signal_set_initialized = false;
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if (!fatal_signal_set_initialized)
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init_fatal_signals ();
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sigemptyset (&fatal_signal_set);
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for (i = 0; i < num_fatal_signals; i++)
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if (fatal_signals[i] >= 0)
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sigaddset (&fatal_signal_set, fatal_signals[i]);
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fatal_signal_set_initialized = true;
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/* Temporarily delay the catchable fatal signals. */
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block_fatal_signals (void)
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init_fatal_signal_set ();
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sigprocmask (SIG_BLOCK, &fatal_signal_set, NULL);
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/* Stop delaying the catchable fatal signals. */
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unblock_fatal_signals (void)
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init_fatal_signal_set ();
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sigprocmask (SIG_UNBLOCK, &fatal_signal_set, NULL);