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Diffstat (limited to 'lib/fatal-signal.c')
| -rw-r--r-- | lib/fatal-signal.c | 362 |
1 files changed, 362 insertions, 0 deletions
diff --git a/lib/fatal-signal.c b/lib/fatal-signal.c new file mode 100644 index 0000000..14ecfe7 --- /dev/null +++ b/lib/fatal-signal.c @@ -0,0 +1,362 @@ +/* Emergency actions in case of a fatal signal. + Copyright (C) 2003-2004, 2006-2020 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 <https://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 "glthread/lock.h" +#include "thread-optim.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) +{ + /* This function is multithread-safe even without synchronization, because + if two threads execute it simultaneously, the fatal_signals[] array will + not change any more after the first of the threads has completed this + function. */ + 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 _GL_ASYNC_SAFE void (*action_t) (int sig); + +/* 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 _GL_ASYNC_SAFE 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 _GL_ASYNC_SAFE 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 (sig); + } + + /* 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]); + } +} + + +/* Lock that makes at_fatal_signal multi-thread safe. */ +gl_lock_define_initialized (static, at_fatal_signal_lock) + +/* Register a cleanup function to be executed when a catchable fatal signal + occurs. */ +void +at_fatal_signal (action_t action) +{ + bool mt = gl_multithreaded (); + + if (mt) gl_lock_lock (at_fatal_signal_lock); + + 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. */ + /* No, we can't do that. If fatal_signal_handler is running in a + different thread and has already fetched the actions pointer (getting + old_actions) but not yet accessed its n-th element, that thread may + crash when accessing an element of the already freed old_actions + array. */ + #if 0 + if (old_actions != static_actions) + free (old_actions); + #endif + } + /* 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++; + + if (mt) gl_lock_unlock (at_fatal_signal_lock); +} + + +/* ========================================================================= */ + + +static sigset_t fatal_signal_set; + +static void +do_init_fatal_signal_set (void) +{ + 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]); +} + +/* Ensure that do_init_fatal_signal_set is called once only. */ +gl_once_define(static, fatal_signal_set_once) + +static void +init_fatal_signal_set (void) +{ + gl_once (fatal_signal_set_once, do_init_fatal_signal_set); +} + +/* Lock and counter that allow block_fatal_signals/unblock_fatal_signals pairs + to occur in different threads and even overlap in time. */ +gl_lock_define_initialized (static, fatal_signals_block_lock) +static unsigned int fatal_signals_block_counter = 0; + +/* Temporarily delay the catchable fatal signals. */ +void +block_fatal_signals (void) +{ + bool mt = gl_multithreaded (); + + if (mt) gl_lock_lock (fatal_signals_block_lock); + + if (fatal_signals_block_counter++ == 0) + { + init_fatal_signal_set (); + sigprocmask (SIG_BLOCK, &fatal_signal_set, NULL); + } + + if (mt) gl_lock_unlock (fatal_signals_block_lock); +} + +/* Stop delaying the catchable fatal signals. */ +void +unblock_fatal_signals (void) +{ + bool mt = gl_multithreaded (); + + if (mt) gl_lock_lock (fatal_signals_block_lock); + + if (fatal_signals_block_counter == 0) + /* There are more calls to unblock_fatal_signals() than to + block_fatal_signals(). */ + abort (); + if (--fatal_signals_block_counter == 0) + { + init_fatal_signal_set (); + sigprocmask (SIG_UNBLOCK, &fatal_signal_set, NULL); + } + + if (mt) gl_lock_unlock (fatal_signals_block_lock); +} + + +unsigned int +get_fatal_signals (int signals[64]) +{ + init_fatal_signal_set (); + + { + int *p = signals; + size_t i; + + for (i = 0; i < num_fatal_signals; i++) + if (fatal_signals[i] >= 0) + *p++ = fatal_signals[i]; + return p - signals; + } +} + +const sigset_t * +get_fatal_signal_set (void) +{ + init_fatal_signal_set (); + return &fatal_signal_set; +} |