sched/signal/sig_deliver.c

/****************************************************************************
 * sched/signal/sig_deliver.c
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.  The
 * ASF licenses this file to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the
 * License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations
 * under the License.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/config.h>

#include <sys/types.h>
#include <signal.h>
#include <unistd.h>
#include <sched.h>
#include <string.h>
#include <debug.h>

#include <nuttx/irq.h>
#include <nuttx/arch.h>
#include <nuttx/signal.h>

#include "signal/signal.h"

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: nxsig_deliver
 *
 * Description:
 *   This function is called on the thread of execution of the signal
 *   receiving task.  It processes all queued signals then returns.
 *
 ****************************************************************************/

void nxsig_deliver(FAR struct tcb_s *stcb)
{
  /* Save the errno.  This must be preserved throughout the signal handling
   * so that the user code final gets the correct errno value (probably
   * EINTR).
   */

  int saved_errno = get_errno();
  int16_t saved_errcode = stcb->errcode;

  FAR sigq_t *sigq;
  sigset_t    savesigprocmask;
  sigset_t    newsigprocmask;
  sigset_t    tmpset1;
  sigset_t    tmpset2;
  irqstate_t  flags;

  /* Loop while there are signals to be delivered */

  for (; ; )
    {
      /* Test if this task is already handling a signal (we don't permit
       * nested signals on the same thread).
       */

      flags = enter_critical_section();
      if ((stcb->flags & TCB_FLAG_SIGNAL_ACTION) != 0)
        {
          /* Yes.. then we must wait for the signal handler to return */

          leave_critical_section(flags);
          break;
        }

      /* Remove the signal structure from the head of the sigpendactionq. */

      sigq  = (FAR sigq_t *)sq_remfirst(&stcb->sigpendactionq);
      if (sigq == NULL)
        {
          /* All queued signal actions have been dispatched */

          leave_critical_section(flags);
          break;
        }

      /* Indicate that a signal is being delivered */

      stcb->flags |= TCB_FLAG_SIGNAL_ACTION;

      sinfo("Deliver signal %d to PID %d\n",
            sigq->info.si_signo, stcb->pid);

      /* Add the signal structure to the sigpostedq.  NOTE:  Since signals
       * are processed one at a time, there should never be more than one
       * signal in the sigpostedq
       */

      sq_addlast((FAR sq_entry_t *)sigq, &(stcb->sigpostedq));

      /* Save a copy of the old sigprocmask and install the new
       * (temporary) sigprocmask.  The new sigprocmask is the union
       * of the current sigprocmask and the sa_mask for the signal being
       * delivered plus the signal being delivered.
       */

      savesigprocmask   = stcb->sigprocmask;
      sigorset(&newsigprocmask, &savesigprocmask, &sigq->mask);
      nxsig_addset(&newsigprocmask, sigq->info.si_signo);
      stcb->sigprocmask = newsigprocmask;

#ifndef CONFIG_BUILD_FLAT
      /* In the kernel build this has to be handled differently if we are
       * dispatching to a signal handler in a user-space task or thread; we
       * have to switch to user-mode before calling the task.
       */

#ifdef CONFIG_SIG_DEFAULT
      /* The default signal action handlers, however always reside in the
       * kernel address space, regardless of configuration.
       */

      if (nxsig_isdefault(stcb, sigq->info.si_signo))
        {
          /* Leave the critical section before calling the handler */

          leave_critical_section(flags);
          (*sigq->action.sighandler)(sigq->info.si_signo, &sigq->info,
                                     NULL);
        }
      else
#endif
      if ((stcb->flags & TCB_FLAG_TTYPE_MASK) != TCB_FLAG_TTYPE_KERNEL)
        {
          siginfo_t info;

          /* The sigq_t pointed to by sigq resides in kernel space.  So we
           * cannot pass a reference to sigq->info to the user application.
           * Instead, we will copy the siginfo_t structure onto the stack.
           * We are currently executing on the stack of the user thread
           * (albeit temporarily in kernel mode), so the copy of the
           * siginfo_t structure will be accessible by the user thread.
           */

          memcpy(&info, &sigq->info, sizeof(siginfo_t));

          /* Leave the critical section before calling the handler */

          leave_critical_section(flags);
          up_signal_dispatch(sigq->action.sighandler, sigq->info.si_signo,
                             &info, NULL);
        }
      else
#endif
        {
          /* The kernel thread signal handler is much simpler. */

          leave_critical_section(flags);
          (*sigq->action.sighandler)(sigq->info.si_signo, &sigq->info,
                                     NULL);
        }

      /* Indicate that a signal has been delivered */

      flags             = enter_critical_section();
      stcb->flags       &= ~TCB_FLAG_SIGNAL_ACTION;

      /* Restore the original sigprocmask.
       *
       * What if the signal handler changed the sigprocmask?  Try to retain
       * any such changes here.
       *
       * REVISIT: This logic is imperfect.  It will fail to detect bits set
       * in the current sigprocmask that were already set by newsigprocmask.
       */

      nxsig_xorset(&tmpset1, &stcb->sigprocmask, &newsigprocmask);
      sigandset(&tmpset2, &stcb->sigprocmask, &tmpset1);
      nxsig_nandset(&tmpset1, &savesigprocmask, &tmpset1);
      sigorset(&stcb->sigprocmask, &tmpset1, &tmpset2);

      /* Remove the signal structure from the sigpostedq */

      sq_rem((FAR sq_entry_t *)sigq, &(stcb->sigpostedq));
      leave_critical_section(flags);

      /* Now, handle the (rare?) case where (a) a blocked signal was
       * received while the signal handling executed but (b) restoring the
       * original sigprocmask will unblock the signal.
       */

      nxsig_unmask_pendingsignal();

      /* Then deallocate the signal structure */

      nxsig_release_pendingsigaction(sigq);
    }

  /* Restore the saved errno value */

  set_errno(saved_errno);
  stcb->errcode = saved_errcode;
}