arch/arm/src/armv6-m/arm_sigdeliver.c

/****************************************************************************
 * arch/arm/src/armv6-m/arm_sigdeliver.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 <stdint.h>
#include <sched.h>
#include <assert.h>
#include <debug.h>

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

#include "sched/sched.h"
#include "arm_internal.h"

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

/****************************************************************************
 * Name: arm_sigdeliver
 *
 * Description:
 *   This is the a signal handling trampoline.  When a signal action was
 *   posted.  The task context was mucked with and forced to branch to this
 *   location with interrupts disabled.
 *
 ****************************************************************************/

void arm_sigdeliver(void)
{
  struct tcb_s *rtcb = this_task();
  uint32_t *regs = rtcb->xcp.saved_regs;

#ifdef CONFIG_SMP
  /* In the SMP case, we must terminate the critical section while the signal
   * handler executes, but we also need to restore the irqcount when the
   * we resume the main thread of the task.
   */

  int16_t saved_irqcount;
#endif

  board_autoled_on(LED_SIGNAL);

  sinfo("rtcb=%p sigdeliver=%p sigpendactionq.head=%p\n",
        rtcb, rtcb->sigdeliver, rtcb->sigpendactionq.head);
  DEBUGASSERT(rtcb->sigdeliver != NULL);

retry:
#ifdef CONFIG_SMP
  /* In the SMP case, up_schedule_sigaction(0) will have incremented
   * 'irqcount' in order to force us into a critical section.  Save the
   * pre-incremented irqcount.
   */

  saved_irqcount = rtcb->irqcount;
  DEBUGASSERT(saved_irqcount >= 0);

  /* Now we need call leave_critical_section() repeatedly to get the irqcount
   * to zero, freeing all global spinlocks that enforce the critical section.
   */

  while (rtcb->irqcount > 0)
    {
      leave_critical_section((uint16_t)regs[REG_PRIMASK]);
    }
#endif /* CONFIG_SMP */

#ifndef CONFIG_SUPPRESS_INTERRUPTS
  /* Then make sure that interrupts are enabled.  Signal handlers must always
   * run with interrupts enabled.
   */

  up_irq_enable();
#endif

  /* Deliver the signal */

  (rtcb->sigdeliver)(rtcb);

  /* Output any debug messages BEFORE restoring errno (because they may
   * alter errno), then disable interrupts again and restore the original
   * errno that is needed by the user logic (it is probably EINTR).
   *
   * I would prefer that all interrupts are disabled when
   * arm_fullcontextrestore() is called, but that may not be necessary.
   */

  sinfo("Resuming\n");

#ifdef CONFIG_SMP
  /* Restore the saved 'irqcount' and recover the critical section
   * spinlocks.
   */

  DEBUGASSERT(rtcb->irqcount == 0);
  while (rtcb->irqcount < saved_irqcount + 1)
    {
      enter_critical_section();
    }
#endif

#ifndef CONFIG_SUPPRESS_INTERRUPTS
  up_irq_save();
#endif

  if (!sq_empty(&rtcb->sigpendactionq) &&
      (rtcb->flags & TCB_FLAG_SIGNAL_ACTION) == 0)
    {
#ifdef CONFIG_SMP
      leave_critical_section((uint16_t)regs[REG_PRIMASK]);
#endif
      goto retry;
    }

  /* Modify the saved return state with the actual saved values in the
   * TCB.  This depends on the fact that nested signal handling is
   * not supported.  Therefore, these values will persist throughout the
   * signal handling action.
   *
   * Keeping this data in the TCB resolves a security problem in protected
   * and kernel mode:  The regs[] array is visible on the user stack and
   * could be modified by a hostile program.
   */

  rtcb->sigdeliver = NULL;  /* Allows next handler to be scheduled */

  /* Then restore the correct state for this thread of
   * execution.
   */

  board_autoled_off(LED_SIGNAL);
#ifdef CONFIG_SMP
  /* We need to keep the IRQ lock until task switching */

  leave_critical_section(up_irq_save());
#endif

  g_running_tasks[this_cpu()] = NULL;
  rtcb->xcp.regs = rtcb->xcp.saved_regs;
  arm_fullcontextrestore();
  UNUSED(regs);
}