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/* Emergency actions in case of a fatal signal.
Copyright (C) 2003-2004, 2006-2015 Free Software Foundation, Inc.
Written by Bruno Haible <bruno@clisp.org>, 2003.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
#include <config.h>
/* Specification. */
#include "fatal-signal.h"
#include <stdbool.h>
#include <stdlib.h>
#include <signal.h>
#include <unistd.h>
#include "sig-handler.h"
#include "xalloc.h"
#define SIZEOF(a) (sizeof(a) / sizeof(a[0]))
/* ========================================================================= */
/* The list of fatal signals.
These are those signals whose default action is to terminate the process
without a core dump, except
SIGKILL - because it cannot be caught,
SIGALRM SIGUSR1 SIGUSR2 SIGPOLL SIGIO SIGLOST - because applications
often use them for their own purpose,
SIGPROF SIGVTALRM - because they are used for profiling,
SIGSTKFLT - because it is more similar to SIGFPE, SIGSEGV, SIGBUS,
SIGSYS - because it is more similar to SIGABRT, SIGSEGV,
SIGPWR - because it of too special use,
SIGRTMIN...SIGRTMAX - because they are reserved for application use.
plus
SIGXCPU, SIGXFSZ - because they are quite similar to SIGTERM. */
static int fatal_signals[] =
{
/* ISO C 99 signals. */
#ifdef SIGINT
SIGINT,
#endif
#ifdef SIGTERM
SIGTERM,
#endif
/* POSIX:2001 signals. */
#ifdef SIGHUP
SIGHUP,
#endif
#ifdef SIGPIPE
SIGPIPE,
#endif
/* BSD signals. */
#ifdef SIGXCPU
SIGXCPU,
#endif
#ifdef SIGXFSZ
SIGXFSZ,
#endif
/* Native Windows signals. */
#ifdef SIGBREAK
SIGBREAK,
#endif
0
};
#define num_fatal_signals (SIZEOF (fatal_signals) - 1)
/* Eliminate signals whose signal handler is SIG_IGN. */
static void
init_fatal_signals (void)
{
static bool fatal_signals_initialized = false;
if (!fatal_signals_initialized)
{
size_t i;
for (i = 0; i < num_fatal_signals; i++)
{
struct sigaction action;
if (sigaction (fatal_signals[i], NULL, &action) >= 0
&& get_handler (&action) == SIG_IGN)
fatal_signals[i] = -1;
}
fatal_signals_initialized = true;
}
}
/* ========================================================================= */
typedef void (*action_t) (void);
/* Type of an entry in the actions array.
The 'action' field is accessed from within the fatal_signal_handler(),
therefore we mark it as 'volatile'. */
typedef struct
{
volatile action_t action;
}
actions_entry_t;
/* The registered cleanup actions. */
static actions_entry_t static_actions[32];
static actions_entry_t * volatile actions = static_actions;
static sig_atomic_t volatile actions_count = 0;
static size_t actions_allocated = SIZEOF (static_actions);
/* The saved signal handlers.
Size 32 would not be sufficient: On HP-UX, SIGXCPU = 33, SIGXFSZ = 34. */
static struct sigaction saved_sigactions[64];
/* Uninstall the handlers. */
static void
uninstall_handlers (void)
{
size_t i;
for (i = 0; i < num_fatal_signals; i++)
if (fatal_signals[i] >= 0)
{
int sig = fatal_signals[i];
if (saved_sigactions[sig].sa_handler == SIG_IGN)
saved_sigactions[sig].sa_handler = SIG_DFL;
sigaction (sig, &saved_sigactions[sig], NULL);
}
}
/* The signal handler. It gets called asynchronously. */
static void
fatal_signal_handler (int sig)
{
for (;;)
{
/* Get the last registered cleanup action, in a reentrant way. */
action_t action;
size_t n = actions_count;
if (n == 0)
break;
n--;
actions_count = n;
action = actions[n].action;
/* Execute the action. */
action ();
}
/* Now execute the signal's default action.
If the signal being delivered was blocked, the re-raised signal would be
delivered when this handler returns. But the way we install this handler,
no signal is blocked, and the re-raised signal is delivered already
during raise(). */
uninstall_handlers ();
raise (sig);
}
/* Install the handlers. */
static void
install_handlers (void)
{
size_t i;
struct sigaction action;
action.sa_handler = &fatal_signal_handler;
/* If we get a fatal signal while executing fatal_signal_handler, enter
fatal_signal_handler recursively, since it is reentrant. Hence no
SA_RESETHAND. */
action.sa_flags = SA_NODEFER;
sigemptyset (&action.sa_mask);
for (i = 0; i < num_fatal_signals; i++)
if (fatal_signals[i] >= 0)
{
int sig = fatal_signals[i];
if (!(sig < sizeof (saved_sigactions) / sizeof (saved_sigactions[0])))
abort ();
sigaction (sig, &action, &saved_sigactions[sig]);
}
}
/* Register a cleanup function to be executed when a catchable fatal signal
occurs. */
void
at_fatal_signal (action_t action)
{
static bool cleanup_initialized = false;
if (!cleanup_initialized)
{
init_fatal_signals ();
install_handlers ();
cleanup_initialized = true;
}
if (actions_count == actions_allocated)
{
/* Extend the actions array. Note that we cannot use xrealloc(),
because then the cleanup() function could access an already
deallocated array. */
actions_entry_t *old_actions = actions;
size_t old_actions_allocated = actions_allocated;
size_t new_actions_allocated = 2 * actions_allocated;
actions_entry_t *new_actions =
XNMALLOC (new_actions_allocated, actions_entry_t);
size_t k;
/* Don't use memcpy() here, because memcpy takes non-volatile arguments
and is therefore not guaranteed to complete all memory stores before
the next statement. */
for (k = 0; k < old_actions_allocated; k++)
new_actions[k] = old_actions[k];
actions = new_actions;
actions_allocated = new_actions_allocated;
/* Now we can free the old actions array. */
if (old_actions != static_actions)
free (old_actions);
}
/* The two uses of 'volatile' in the types above (and ISO C 99 section
5.1.2.3.(5)) ensure that we increment the actions_count only after
the new action has been written to the memory location
actions[actions_count]. */
actions[actions_count].action = action;
actions_count++;
}
/* ========================================================================= */
static sigset_t fatal_signal_set;
static void
init_fatal_signal_set (void)
{
static bool fatal_signal_set_initialized = false;
if (!fatal_signal_set_initialized)
{
size_t i;
init_fatal_signals ();
sigemptyset (&fatal_signal_set);
for (i = 0; i < num_fatal_signals; i++)
if (fatal_signals[i] >= 0)
sigaddset (&fatal_signal_set, fatal_signals[i]);
fatal_signal_set_initialized = true;
}
}
/* Temporarily delay the catchable fatal signals. */
void
block_fatal_signals (void)
{
init_fatal_signal_set ();
sigprocmask (SIG_BLOCK, &fatal_signal_set, NULL);
}
/* Stop delaying the catchable fatal signals. */
void
unblock_fatal_signals (void)
{
init_fatal_signal_set ();
sigprocmask (SIG_UNBLOCK, &fatal_signal_set, NULL);
}
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