105436638acc7c010349a69c3395f1a57c642dc62Ying Wang/* POSIX compatible signal blocking. 205436638acc7c010349a69c3395f1a57c642dc62Ying Wang Copyright (C) 2008-2012 Free Software Foundation, Inc. 305436638acc7c010349a69c3395f1a57c642dc62Ying Wang Written by Eric Blake <ebb9@byu.net>, 2008. 405436638acc7c010349a69c3395f1a57c642dc62Ying Wang 505436638acc7c010349a69c3395f1a57c642dc62Ying Wang This program is free software: you can redistribute it and/or modify 605436638acc7c010349a69c3395f1a57c642dc62Ying Wang it under the terms of the GNU General Public License as published by 705436638acc7c010349a69c3395f1a57c642dc62Ying Wang the Free Software Foundation; either version 3 of the License, or 805436638acc7c010349a69c3395f1a57c642dc62Ying Wang (at your option) any later version. 905436638acc7c010349a69c3395f1a57c642dc62Ying Wang 1005436638acc7c010349a69c3395f1a57c642dc62Ying Wang This program is distributed in the hope that it will be useful, 1105436638acc7c010349a69c3395f1a57c642dc62Ying Wang but WITHOUT ANY WARRANTY; without even the implied warranty of 1205436638acc7c010349a69c3395f1a57c642dc62Ying Wang MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 1305436638acc7c010349a69c3395f1a57c642dc62Ying Wang GNU General Public License for more details. 1405436638acc7c010349a69c3395f1a57c642dc62Ying Wang 1505436638acc7c010349a69c3395f1a57c642dc62Ying Wang You should have received a copy of the GNU General Public License 1605436638acc7c010349a69c3395f1a57c642dc62Ying Wang along with this program. If not, see <http://www.gnu.org/licenses/>. */ 1705436638acc7c010349a69c3395f1a57c642dc62Ying Wang 1805436638acc7c010349a69c3395f1a57c642dc62Ying Wang#include <config.h> 1905436638acc7c010349a69c3395f1a57c642dc62Ying Wang 2005436638acc7c010349a69c3395f1a57c642dc62Ying Wang/* Specification. */ 2105436638acc7c010349a69c3395f1a57c642dc62Ying Wang#include <signal.h> 2205436638acc7c010349a69c3395f1a57c642dc62Ying Wang 2305436638acc7c010349a69c3395f1a57c642dc62Ying Wang#include <errno.h> 2405436638acc7c010349a69c3395f1a57c642dc62Ying Wang#include <stdint.h> 2505436638acc7c010349a69c3395f1a57c642dc62Ying Wang#include <stdlib.h> 2605436638acc7c010349a69c3395f1a57c642dc62Ying Wang 2705436638acc7c010349a69c3395f1a57c642dc62Ying Wang/* This implementation of sigaction is tailored to native Windows behavior: 2805436638acc7c010349a69c3395f1a57c642dc62Ying Wang signal() has SysV semantics (ie. the handler is uninstalled before 2905436638acc7c010349a69c3395f1a57c642dc62Ying Wang it is invoked). This is an inherent data race if an asynchronous 3005436638acc7c010349a69c3395f1a57c642dc62Ying Wang signal is sent twice in a row before we can reinstall our handler, 3105436638acc7c010349a69c3395f1a57c642dc62Ying Wang but there's nothing we can do about it. Meanwhile, sigprocmask() 3205436638acc7c010349a69c3395f1a57c642dc62Ying Wang is not present, and while we can use the gnulib replacement to 3305436638acc7c010349a69c3395f1a57c642dc62Ying Wang provide critical sections, it too suffers from potential data races 3405436638acc7c010349a69c3395f1a57c642dc62Ying Wang in the face of an ill-timed asynchronous signal. And we compound 3505436638acc7c010349a69c3395f1a57c642dc62Ying Wang the situation by reading static storage in a signal handler, which 3605436638acc7c010349a69c3395f1a57c642dc62Ying Wang POSIX warns is not generically async-signal-safe. Oh well. 3705436638acc7c010349a69c3395f1a57c642dc62Ying Wang 3805436638acc7c010349a69c3395f1a57c642dc62Ying Wang Additionally: 3905436638acc7c010349a69c3395f1a57c642dc62Ying Wang - We don't implement SA_NOCLDSTOP or SA_NOCLDWAIT, because SIGCHLD 4005436638acc7c010349a69c3395f1a57c642dc62Ying Wang is not defined. 4105436638acc7c010349a69c3395f1a57c642dc62Ying Wang - We don't implement SA_ONSTACK, because sigaltstack() is not present. 4205436638acc7c010349a69c3395f1a57c642dc62Ying Wang - We ignore SA_RESTART, because blocking native Windows API calls are 4305436638acc7c010349a69c3395f1a57c642dc62Ying Wang not interrupted anyway when an asynchronous signal occurs, and the 4405436638acc7c010349a69c3395f1a57c642dc62Ying Wang MSVCRT runtime never sets errno to EINTR. 4505436638acc7c010349a69c3395f1a57c642dc62Ying Wang - We don't implement SA_SIGINFO because it is impossible to do so 4605436638acc7c010349a69c3395f1a57c642dc62Ying Wang portably. 4705436638acc7c010349a69c3395f1a57c642dc62Ying Wang 4805436638acc7c010349a69c3395f1a57c642dc62Ying Wang POSIX states that an application should not mix signal() and 4905436638acc7c010349a69c3395f1a57c642dc62Ying Wang sigaction(). We support the use of signal() within the gnulib 5005436638acc7c010349a69c3395f1a57c642dc62Ying Wang sigprocmask() substitute, but all other application code linked 5105436638acc7c010349a69c3395f1a57c642dc62Ying Wang with this module should stick with only sigaction(). */ 5205436638acc7c010349a69c3395f1a57c642dc62Ying Wang 5305436638acc7c010349a69c3395f1a57c642dc62Ying Wang/* Check some of our assumptions. */ 5405436638acc7c010349a69c3395f1a57c642dc62Ying Wang#if defined SIGCHLD || defined HAVE_SIGALTSTACK || defined HAVE_SIGINTERRUPT 5505436638acc7c010349a69c3395f1a57c642dc62Ying Wang# error "Revisit the assumptions made in the sigaction module" 5605436638acc7c010349a69c3395f1a57c642dc62Ying Wang#endif 5705436638acc7c010349a69c3395f1a57c642dc62Ying Wang 5805436638acc7c010349a69c3395f1a57c642dc62Ying Wang/* Out-of-range substitutes make a good fallback for uncatchable 5905436638acc7c010349a69c3395f1a57c642dc62Ying Wang signals. */ 6005436638acc7c010349a69c3395f1a57c642dc62Ying Wang#ifndef SIGKILL 6105436638acc7c010349a69c3395f1a57c642dc62Ying Wang# define SIGKILL (-1) 6205436638acc7c010349a69c3395f1a57c642dc62Ying Wang#endif 6305436638acc7c010349a69c3395f1a57c642dc62Ying Wang#ifndef SIGSTOP 6405436638acc7c010349a69c3395f1a57c642dc62Ying Wang# define SIGSTOP (-1) 6505436638acc7c010349a69c3395f1a57c642dc62Ying Wang#endif 6605436638acc7c010349a69c3395f1a57c642dc62Ying Wang 6705436638acc7c010349a69c3395f1a57c642dc62Ying Wang/* On native Windows, as of 2008, the signal SIGABRT_COMPAT is an alias 6805436638acc7c010349a69c3395f1a57c642dc62Ying Wang for the signal SIGABRT. Only one signal handler is stored for both 6905436638acc7c010349a69c3395f1a57c642dc62Ying Wang SIGABRT and SIGABRT_COMPAT. SIGABRT_COMPAT is not a signal of its own. */ 7005436638acc7c010349a69c3395f1a57c642dc62Ying Wang#if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__ 7105436638acc7c010349a69c3395f1a57c642dc62Ying Wang# undef SIGABRT_COMPAT 7205436638acc7c010349a69c3395f1a57c642dc62Ying Wang# define SIGABRT_COMPAT 6 7305436638acc7c010349a69c3395f1a57c642dc62Ying Wang#endif 7405436638acc7c010349a69c3395f1a57c642dc62Ying Wang 7505436638acc7c010349a69c3395f1a57c642dc62Ying Wang/* A signal handler. */ 7605436638acc7c010349a69c3395f1a57c642dc62Ying Wangtypedef void (*handler_t) (int signal); 7705436638acc7c010349a69c3395f1a57c642dc62Ying Wang 7805436638acc7c010349a69c3395f1a57c642dc62Ying Wang/* Set of current actions. If sa_handler for an entry is NULL, then 7905436638acc7c010349a69c3395f1a57c642dc62Ying Wang that signal is not currently handled by the sigaction handler. */ 8005436638acc7c010349a69c3395f1a57c642dc62Ying Wangstatic struct sigaction volatile action_array[NSIG] /* = 0 */; 8105436638acc7c010349a69c3395f1a57c642dc62Ying Wang 8205436638acc7c010349a69c3395f1a57c642dc62Ying Wang/* Signal handler that is installed for signals. */ 8305436638acc7c010349a69c3395f1a57c642dc62Ying Wangstatic void 8405436638acc7c010349a69c3395f1a57c642dc62Ying Wangsigaction_handler (int sig) 8505436638acc7c010349a69c3395f1a57c642dc62Ying Wang{ 8605436638acc7c010349a69c3395f1a57c642dc62Ying Wang handler_t handler; 8705436638acc7c010349a69c3395f1a57c642dc62Ying Wang sigset_t mask; 8805436638acc7c010349a69c3395f1a57c642dc62Ying Wang sigset_t oldmask; 8905436638acc7c010349a69c3395f1a57c642dc62Ying Wang int saved_errno = errno; 9005436638acc7c010349a69c3395f1a57c642dc62Ying Wang if (sig < 0 || NSIG <= sig || !action_array[sig].sa_handler) 9105436638acc7c010349a69c3395f1a57c642dc62Ying Wang { 9205436638acc7c010349a69c3395f1a57c642dc62Ying Wang /* Unexpected situation; be careful to avoid recursive abort. */ 9305436638acc7c010349a69c3395f1a57c642dc62Ying Wang if (sig == SIGABRT) 9405436638acc7c010349a69c3395f1a57c642dc62Ying Wang signal (SIGABRT, SIG_DFL); 9505436638acc7c010349a69c3395f1a57c642dc62Ying Wang abort (); 9605436638acc7c010349a69c3395f1a57c642dc62Ying Wang } 9705436638acc7c010349a69c3395f1a57c642dc62Ying Wang 9805436638acc7c010349a69c3395f1a57c642dc62Ying Wang /* Reinstall the signal handler when required; otherwise update the 9905436638acc7c010349a69c3395f1a57c642dc62Ying Wang bookkeeping so that the user's handler may call sigaction and get 10005436638acc7c010349a69c3395f1a57c642dc62Ying Wang accurate results. We know the signal isn't currently blocked, or 10105436638acc7c010349a69c3395f1a57c642dc62Ying Wang we wouldn't be in its handler, therefore we know that we are not 10205436638acc7c010349a69c3395f1a57c642dc62Ying Wang interrupting a sigaction() call. There is a race where any 10305436638acc7c010349a69c3395f1a57c642dc62Ying Wang asynchronous instance of the same signal occurring before we 10405436638acc7c010349a69c3395f1a57c642dc62Ying Wang reinstall the handler will trigger the default handler; oh 10505436638acc7c010349a69c3395f1a57c642dc62Ying Wang well. */ 10605436638acc7c010349a69c3395f1a57c642dc62Ying Wang handler = action_array[sig].sa_handler; 10705436638acc7c010349a69c3395f1a57c642dc62Ying Wang if ((action_array[sig].sa_flags & SA_RESETHAND) == 0) 10805436638acc7c010349a69c3395f1a57c642dc62Ying Wang signal (sig, sigaction_handler); 10905436638acc7c010349a69c3395f1a57c642dc62Ying Wang else 11005436638acc7c010349a69c3395f1a57c642dc62Ying Wang action_array[sig].sa_handler = NULL; 11105436638acc7c010349a69c3395f1a57c642dc62Ying Wang 11205436638acc7c010349a69c3395f1a57c642dc62Ying Wang /* Block appropriate signals. */ 11305436638acc7c010349a69c3395f1a57c642dc62Ying Wang mask = action_array[sig].sa_mask; 11405436638acc7c010349a69c3395f1a57c642dc62Ying Wang if ((action_array[sig].sa_flags & SA_NODEFER) == 0) 11505436638acc7c010349a69c3395f1a57c642dc62Ying Wang sigaddset (&mask, sig); 11605436638acc7c010349a69c3395f1a57c642dc62Ying Wang sigprocmask (SIG_BLOCK, &mask, &oldmask); 11705436638acc7c010349a69c3395f1a57c642dc62Ying Wang 11805436638acc7c010349a69c3395f1a57c642dc62Ying Wang /* Invoke the user's handler, then restore prior mask. */ 11905436638acc7c010349a69c3395f1a57c642dc62Ying Wang errno = saved_errno; 12005436638acc7c010349a69c3395f1a57c642dc62Ying Wang handler (sig); 12105436638acc7c010349a69c3395f1a57c642dc62Ying Wang saved_errno = errno; 12205436638acc7c010349a69c3395f1a57c642dc62Ying Wang sigprocmask (SIG_SETMASK, &oldmask, NULL); 12305436638acc7c010349a69c3395f1a57c642dc62Ying Wang errno = saved_errno; 12405436638acc7c010349a69c3395f1a57c642dc62Ying Wang} 12505436638acc7c010349a69c3395f1a57c642dc62Ying Wang 12605436638acc7c010349a69c3395f1a57c642dc62Ying Wang/* Change and/or query the action that will be taken on delivery of 12705436638acc7c010349a69c3395f1a57c642dc62Ying Wang signal SIG. If not NULL, ACT describes the new behavior. If not 12805436638acc7c010349a69c3395f1a57c642dc62Ying Wang NULL, OACT is set to the prior behavior. Return 0 on success, or 12905436638acc7c010349a69c3395f1a57c642dc62Ying Wang set errno and return -1 on failure. */ 13005436638acc7c010349a69c3395f1a57c642dc62Ying Wangint 13105436638acc7c010349a69c3395f1a57c642dc62Ying Wangsigaction (int sig, const struct sigaction *restrict act, 13205436638acc7c010349a69c3395f1a57c642dc62Ying Wang struct sigaction *restrict oact) 13305436638acc7c010349a69c3395f1a57c642dc62Ying Wang{ 13405436638acc7c010349a69c3395f1a57c642dc62Ying Wang sigset_t mask; 13505436638acc7c010349a69c3395f1a57c642dc62Ying Wang sigset_t oldmask; 13605436638acc7c010349a69c3395f1a57c642dc62Ying Wang int saved_errno; 13705436638acc7c010349a69c3395f1a57c642dc62Ying Wang 13805436638acc7c010349a69c3395f1a57c642dc62Ying Wang if (sig < 0 || NSIG <= sig || sig == SIGKILL || sig == SIGSTOP 13905436638acc7c010349a69c3395f1a57c642dc62Ying Wang || (act && act->sa_handler == SIG_ERR)) 14005436638acc7c010349a69c3395f1a57c642dc62Ying Wang { 14105436638acc7c010349a69c3395f1a57c642dc62Ying Wang errno = EINVAL; 14205436638acc7c010349a69c3395f1a57c642dc62Ying Wang return -1; 14305436638acc7c010349a69c3395f1a57c642dc62Ying Wang } 14405436638acc7c010349a69c3395f1a57c642dc62Ying Wang 14505436638acc7c010349a69c3395f1a57c642dc62Ying Wang#ifdef SIGABRT_COMPAT 14605436638acc7c010349a69c3395f1a57c642dc62Ying Wang if (sig == SIGABRT_COMPAT) 14705436638acc7c010349a69c3395f1a57c642dc62Ying Wang sig = SIGABRT; 14805436638acc7c010349a69c3395f1a57c642dc62Ying Wang#endif 14905436638acc7c010349a69c3395f1a57c642dc62Ying Wang 15005436638acc7c010349a69c3395f1a57c642dc62Ying Wang /* POSIX requires sigaction() to be async-signal-safe. In other 15105436638acc7c010349a69c3395f1a57c642dc62Ying Wang words, if an asynchronous signal can occur while we are anywhere 15205436638acc7c010349a69c3395f1a57c642dc62Ying Wang inside this function, the user's handler could then call 15305436638acc7c010349a69c3395f1a57c642dc62Ying Wang sigaction() recursively and expect consistent results. We meet 15405436638acc7c010349a69c3395f1a57c642dc62Ying Wang this rule by using sigprocmask to block all signals before 15505436638acc7c010349a69c3395f1a57c642dc62Ying Wang modifying any data structure that could be read from a signal 15605436638acc7c010349a69c3395f1a57c642dc62Ying Wang handler; this works since we know that the gnulib sigprocmask 15705436638acc7c010349a69c3395f1a57c642dc62Ying Wang replacement does not try to use sigaction() from its handler. */ 15805436638acc7c010349a69c3395f1a57c642dc62Ying Wang if (!act && !oact) 15905436638acc7c010349a69c3395f1a57c642dc62Ying Wang return 0; 16005436638acc7c010349a69c3395f1a57c642dc62Ying Wang sigfillset (&mask); 16105436638acc7c010349a69c3395f1a57c642dc62Ying Wang sigprocmask (SIG_BLOCK, &mask, &oldmask); 16205436638acc7c010349a69c3395f1a57c642dc62Ying Wang if (oact) 16305436638acc7c010349a69c3395f1a57c642dc62Ying Wang { 16405436638acc7c010349a69c3395f1a57c642dc62Ying Wang if (action_array[sig].sa_handler) 16505436638acc7c010349a69c3395f1a57c642dc62Ying Wang *oact = action_array[sig]; 16605436638acc7c010349a69c3395f1a57c642dc62Ying Wang else 16705436638acc7c010349a69c3395f1a57c642dc62Ying Wang { 16805436638acc7c010349a69c3395f1a57c642dc62Ying Wang /* Safe to change the handler at will here, since all 16905436638acc7c010349a69c3395f1a57c642dc62Ying Wang signals are currently blocked. */ 17005436638acc7c010349a69c3395f1a57c642dc62Ying Wang oact->sa_handler = signal (sig, SIG_DFL); 17105436638acc7c010349a69c3395f1a57c642dc62Ying Wang if (oact->sa_handler == SIG_ERR) 17205436638acc7c010349a69c3395f1a57c642dc62Ying Wang goto failure; 17305436638acc7c010349a69c3395f1a57c642dc62Ying Wang signal (sig, oact->sa_handler); 17405436638acc7c010349a69c3395f1a57c642dc62Ying Wang oact->sa_flags = SA_RESETHAND | SA_NODEFER; 17505436638acc7c010349a69c3395f1a57c642dc62Ying Wang sigemptyset (&oact->sa_mask); 17605436638acc7c010349a69c3395f1a57c642dc62Ying Wang } 17705436638acc7c010349a69c3395f1a57c642dc62Ying Wang } 17805436638acc7c010349a69c3395f1a57c642dc62Ying Wang 17905436638acc7c010349a69c3395f1a57c642dc62Ying Wang if (act) 18005436638acc7c010349a69c3395f1a57c642dc62Ying Wang { 18105436638acc7c010349a69c3395f1a57c642dc62Ying Wang /* Safe to install the handler before updating action_array, 18205436638acc7c010349a69c3395f1a57c642dc62Ying Wang since all signals are currently blocked. */ 18305436638acc7c010349a69c3395f1a57c642dc62Ying Wang if (act->sa_handler == SIG_DFL || act->sa_handler == SIG_IGN) 18405436638acc7c010349a69c3395f1a57c642dc62Ying Wang { 18505436638acc7c010349a69c3395f1a57c642dc62Ying Wang if (signal (sig, act->sa_handler) == SIG_ERR) 18605436638acc7c010349a69c3395f1a57c642dc62Ying Wang goto failure; 18705436638acc7c010349a69c3395f1a57c642dc62Ying Wang action_array[sig].sa_handler = NULL; 18805436638acc7c010349a69c3395f1a57c642dc62Ying Wang } 18905436638acc7c010349a69c3395f1a57c642dc62Ying Wang else 19005436638acc7c010349a69c3395f1a57c642dc62Ying Wang { 19105436638acc7c010349a69c3395f1a57c642dc62Ying Wang if (signal (sig, sigaction_handler) == SIG_ERR) 19205436638acc7c010349a69c3395f1a57c642dc62Ying Wang goto failure; 19305436638acc7c010349a69c3395f1a57c642dc62Ying Wang action_array[sig] = *act; 19405436638acc7c010349a69c3395f1a57c642dc62Ying Wang } 19505436638acc7c010349a69c3395f1a57c642dc62Ying Wang } 19605436638acc7c010349a69c3395f1a57c642dc62Ying Wang sigprocmask (SIG_SETMASK, &oldmask, NULL); 19705436638acc7c010349a69c3395f1a57c642dc62Ying Wang return 0; 19805436638acc7c010349a69c3395f1a57c642dc62Ying Wang 19905436638acc7c010349a69c3395f1a57c642dc62Ying Wang failure: 20005436638acc7c010349a69c3395f1a57c642dc62Ying Wang saved_errno = errno; 20105436638acc7c010349a69c3395f1a57c642dc62Ying Wang sigprocmask (SIG_SETMASK, &oldmask, NULL); 20205436638acc7c010349a69c3395f1a57c642dc62Ying Wang errno = saved_errno; 20305436638acc7c010349a69c3395f1a57c642dc62Ying Wang return -1; 20405436638acc7c010349a69c3395f1a57c642dc62Ying Wang} 205