/* POSIX compatible signal blocking.

   Copyright (C) 2006-2020 Free Software Foundation, Inc.

   Written by Bruno Haible <bruno@clisp.org>, 2006.

   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 <signal.h>

#include <errno.h>

#include <stdint.h>

#include <stdlib.h>

#if HAVE_MSVC_INVALID_PARAMETER_HANDLER

# include "msvc-inval.h"

#endif

/* We assume that a platform without POSIX signal blocking functions

   also does not have the POSIX sigaction() function, only the

   signal() function.  We also assume signal() has SysV semantics,

   where any handler is uninstalled prior to being invoked.  This is

   true for native Windows platforms.  */

/* We use raw signal(), but also provide a wrapper rpl_signal() so

   that applications can query or change a blocked signal.  */

#undef signal

/* Provide invalid signal numbers as fallbacks if the uncatchable

   signals are not defined.  */

#ifndef SIGKILL

# define SIGKILL (-1)

#endif

#ifndef SIGSTOP

# define SIGSTOP (-1)

#endif

/* On native Windows, as of 2008, the signal SIGABRT_COMPAT is an alias

   for the signal SIGABRT.  Only one signal handler is stored for both

   SIGABRT and SIGABRT_COMPAT.  SIGABRT_COMPAT is not a signal of its own.  */

#if defined _WIN32 && ! defined __CYGWIN__

# undef SIGABRT_COMPAT

# define SIGABRT_COMPAT 6

#endif

#ifdef SIGABRT_COMPAT

# define SIGABRT_COMPAT_MASK (1U << SIGABRT_COMPAT)

#else

# define SIGABRT_COMPAT_MASK 0

#endif

typedef void (*handler_t) (int);

#if HAVE_MSVC_INVALID_PARAMETER_HANDLER

static handler_t

signal_nothrow (int sig, handler_t handler)

{

  handler_t result;

  TRY_MSVC_INVAL

    {

      result = signal (sig, handler);

    }

  CATCH_MSVC_INVAL

    {

      result = SIG_ERR;

      errno = EINVAL;

    }

  DONE_MSVC_INVAL;

  return result;

}

# define signal signal_nothrow

#endif

/* Handling of gnulib defined signals.  */

#if GNULIB_defined_SIGPIPE

static handler_t SIGPIPE_handler = SIG_DFL;

#endif

#if GNULIB_defined_SIGPIPE

static handler_t

ext_signal (int sig, handler_t handler)

{

  switch (sig)

    {

    case SIGPIPE:

      {

        handler_t old_handler = SIGPIPE_handler;

        SIGPIPE_handler = handler;

        return old_handler;

      }

    default: /* System defined signal */

      return signal (sig, handler);

    }

}

# undef signal

# define signal ext_signal

#endif

int

sigismember (const sigset_t *set, int sig)

{

  if (sig >= 0 && sig < NSIG)

    {

      #ifdef SIGABRT_COMPAT

      if (sig == SIGABRT_COMPAT)

        sig = SIGABRT;

      #endif

      return (*set >> sig) & 1;

    }

  else

    return 0;

}

int

sigemptyset (sigset_t *set)

{

  *set = 0;

  return 0;

}

int

sigaddset (sigset_t *set, int sig)

{

  if (sig >= 0 && sig < NSIG)

    {

      #ifdef SIGABRT_COMPAT

      if (sig == SIGABRT_COMPAT)

        sig = SIGABRT;

      #endif

      *set |= 1U << sig;

      return 0;

    }

  else

    {

      errno = EINVAL;

      return -1;

    }

}

int

sigdelset (sigset_t *set, int sig)

{

  if (sig >= 0 && sig < NSIG)

    {

      #ifdef SIGABRT_COMPAT

      if (sig == SIGABRT_COMPAT)

        sig = SIGABRT;

      #endif

      *set &= ~(1U << sig);

      return 0;

    }

  else

    {

      errno = EINVAL;

      return -1;

    }

}

int

sigfillset (sigset_t *set)

{

  *set = ((2U << (NSIG - 1)) - 1) & ~ SIGABRT_COMPAT_MASK;

  return 0;

}

/* Set of currently blocked signals.  */

static volatile sigset_t blocked_set /* = 0 */;

/* Set of currently blocked and pending signals.  */

static volatile sig_atomic_t pending_array[NSIG] /* = { 0 } */;

/* Signal handler that is installed for blocked signals.  */

static void

blocked_handler (int sig)

{

  /* Reinstall the handler, in case the signal occurs multiple times

     while blocked.  There is an inherent race where an asynchronous

     signal in between when the kernel uninstalled the handler and

     when we reinstall it will trigger the default handler; oh

     well.  */

  signal (sig, blocked_handler);

  if (sig >= 0 && sig < NSIG)

    pending_array[sig] = 1;

}

int

sigpending (sigset_t *set)

{

  sigset_t pending = 0;

  int sig;

  for (sig = 0; sig < NSIG; sig++)

    if (pending_array[sig])

      pending |= 1U << sig;

  *set = pending;

  return 0;

}

/* The previous signal handlers.

   Only the array elements corresponding to blocked signals are relevant.  */

static volatile handler_t old_handlers[NSIG];

int

sigprocmask (int operation, const sigset_t *set, sigset_t *old_set)

{

  if (old_set != NULL)

    *old_set = blocked_set;

  if (set != NULL)

    {

      sigset_t new_blocked_set;

      sigset_t to_unblock;

      sigset_t to_block;

      switch (operation)

        {

        case SIG_BLOCK:

          new_blocked_set = blocked_set | *set;

          break;

        case SIG_SETMASK:

          new_blocked_set = *set;

          break;

        case SIG_UNBLOCK:

          new_blocked_set = blocked_set & ~*set;

          break;

        default:

          errno = EINVAL;

          return -1;

        }

      to_unblock = blocked_set & ~new_blocked_set;

      to_block = new_blocked_set & ~blocked_set;

      if (to_block != 0)

        {

          int sig;

          for (sig = 0; sig < NSIG; sig++)

            if ((to_block >> sig) & 1)

              {

                pending_array[sig] = 0;

                if ((old_handlers[sig] = signal (sig, blocked_handler)) != SIG_ERR)

                  blocked_set |= 1U << sig;

              }

        }

      if (to_unblock != 0)

        {

          sig_atomic_t received[NSIG];

          int sig;

          for (sig = 0; sig < NSIG; sig++)

            if ((to_unblock >> sig) & 1)

              {

                if (signal (sig, old_handlers[sig]) != blocked_handler)

                  /* The application changed a signal handler while the signal

                     was blocked, bypassing our rpl_signal replacement.

                     We don't support this.  */

                  abort ();

                received[sig] = pending_array[sig];

                blocked_set &= ~(1U << sig);

                pending_array[sig] = 0;

              }

            else

              received[sig] = 0;

          for (sig = 0; sig < NSIG; sig++)

            if (received[sig])

              raise (sig);

        }

    }

  return 0;

}

/* Install the handler FUNC for signal SIG, and return the previous

   handler.  */

handler_t

rpl_signal (int sig, handler_t handler)

{

  /* We must provide a wrapper, so that a user can query what handler

     they installed even if that signal is currently blocked.  */

  if (sig >= 0 && sig < NSIG && sig != SIGKILL && sig != SIGSTOP

      && handler != SIG_ERR)

    {

      #ifdef SIGABRT_COMPAT

      if (sig == SIGABRT_COMPAT)

        sig = SIGABRT;

      #endif

      if (blocked_set & (1U << sig))

        {

          /* POSIX states that sigprocmask and signal are both

             async-signal-safe.  This is not true of our

             implementation - there is a slight data race where an

             asynchronous interrupt on signal A can occur after we

             install blocked_handler but before we have updated

             old_handlers for signal B, such that handler A can see

             stale information if it calls signal(B).  Oh well -

             signal handlers really shouldn't try to manipulate the

             installed handlers of unrelated signals.  */

          handler_t result = old_handlers[sig];

          old_handlers[sig] = handler;

          return result;

        }

      else

        return signal (sig, handler);

    }

  else

    {

      errno = EINVAL;

      return SIG_ERR;

    }

}

#if GNULIB_defined_SIGPIPE

/* Raise the signal SIGPIPE.  */

int

_gl_raise_SIGPIPE (void)

{

  if (blocked_set & (1U << SIGPIPE))

    pending_array[SIGPIPE] = 1;

  else

    {

      handler_t handler = SIGPIPE_handler;

      if (handler == SIG_DFL)

        exit (128 + SIGPIPE);

      else if (handler != SIG_IGN)

        (*handler) (SIGPIPE);

    }

  return 0;

}

#endif