1  /* Tests of signal delivery on an alternate stack (nonlethal).
       2     Copyright (C) 2019-2023 Free Software Foundation, Inc.
       3     This file is part of the GNU C Library.
       4  
       5     The GNU C Library is free software; you can redistribute it and/or
       6     modify it under the terms of the GNU Lesser General Public
       7     License as published by the Free Software Foundation; either
       8     version 2.1 of the License, or (at your option) any later version.
       9  
      10     The GNU C Library is distributed in the hope that it will be useful,
      11     but WITHOUT ANY WARRANTY; without even the implied warranty of
      12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      13     Lesser General Public License for more details.
      14  
      15     You should have received a copy of the GNU Lesser General Public
      16     License along with the GNU C Library; if not, see
      17     <https://www.gnu.org/licenses/>.  */
      18  
      19  #include <support/xsignal.h>
      20  #include <support/support.h>
      21  #include <support/check.h>
      22  
      23  /* C2011 7.4.1.1p5 specifies that only the following operations are
      24     guaranteed to be well-defined inside an asynchronous signal handler:
      25       * any operation on a lock-free atomic object
      26       * assigning a value to an object declared as volatile sig_atomic_t
      27       * calling abort, _Exit, quick_exit, or signal
      28         * signal may only be called with its first argument equal to the
      29           number of the signal that caused the handler to be called
      30  
      31     We use this list as a guideline for the set of operations that ought
      32     also to be safe in a _synchronous_ signal delivered on an alternate
      33     signal stack with only MINSIGSTKSZ bytes of space.
      34  
      35     This test program tests all of the above operations that do not,
      36     one way or another, cause the program to be terminated.  */
      37  
      38  /* We do not try to test atomic operations exhaustively, only a simple
      39     atomic counter increment.  This is only safe if atomic_[u]int is
      40     unconditionally lock-free.  */
      41  #ifdef __STDC_NO_ATOMICS__
      42  # define TEST_ATOMIC_OPS 0
      43  #else
      44  # include <stdatomic.h>
      45  # if ATOMIC_INT_LOCK_FREE != 2
      46  #  define TEST_ATOMIC_OPS 0
      47  # else
      48  #  define TEST_ATOMIC_OPS 1
      49  # endif
      50  #endif
      51  
      52  static volatile sig_atomic_t signal_flag = 0;
      53  static volatile sig_atomic_t signal_err = 0;
      54  static void
      55  handler_set_flag (int unused)
      56  {
      57    signal_flag = 1;
      58  }
      59  
      60  static void
      61  handler_set_flag_once (int sig)
      62  {
      63    signal_flag = 1;
      64    if (signal (sig, SIG_IGN) == SIG_ERR)
      65      /* It is not safe to call FAIL_EXIT1 here.  Set another flag instead.  */
      66      signal_err = 1;
      67  }
      68  
      69  #if TEST_ATOMIC_OPS
      70  static atomic_uint signal_count = 0;
      71  static void
      72  handler_count_up_1 (int unused)
      73  {
      74    atomic_fetch_add (&signal_count, 1);
      75  }
      76  #endif
      77  
      78  int
      79  do_test (void)
      80  {
      81    void *sstk = xalloc_sigstack (0);
      82    struct sigaction sa;
      83  
      84    /* Test 1: setting a volatile sig_atomic_t flag.  */
      85    sa.sa_handler = handler_set_flag;
      86    sa.sa_flags   = SA_RESTART | SA_ONSTACK;
      87    sigfillset (&sa.sa_mask);
      88    if (sigaction (SIGUSR1, &sa, 0))
      89      FAIL_EXIT1 ("sigaction (SIGUSR1, handler_set_flag): %m\n");
      90  
      91    TEST_VERIFY_EXIT (signal_flag == 0);
      92    raise (SIGUSR1);
      93    TEST_VERIFY_EXIT (signal_flag == 1);
      94    signal_flag = 0;
      95    raise (SIGUSR1);
      96    TEST_VERIFY_EXIT (signal_flag == 1);
      97    signal_flag = 0;
      98  
      99    /* Test 1: setting a volatile sig_atomic_t flag and then ignoring
     100       further delivery of the signal. */
     101    sa.sa_handler = handler_set_flag_once;
     102    if (sigaction (SIGUSR1, &sa, 0))
     103      FAIL_EXIT1 ("sigaction (SIGUSR1, handler_set_flag_once): %m\n");
     104  
     105    raise (SIGUSR1);
     106    TEST_VERIFY_EXIT (signal_flag == 1);
     107    /* Note: if signal_err is 1, a system call failed, but we can't
     108       report the error code because errno is indeterminate.  */
     109    TEST_VERIFY_EXIT (signal_err == 0);
     110  
     111    signal_flag = 0;
     112    raise (SIGUSR1);
     113    TEST_VERIFY_EXIT (signal_flag == 0);
     114    TEST_VERIFY_EXIT (signal_err == 0);
     115  
     116  #if TEST_ATOMIC_OPS
     117    sa.sa_handler = handler_count_up_1;
     118    if (sigaction (SIGUSR1, &sa, 0))
     119      FAIL_EXIT1 ("sigaction (SIGUSR1, handler_count_up_1): %m\n");
     120  
     121    raise (SIGUSR1);
     122    TEST_VERIFY_EXIT (atomic_load (&signal_count) == 1);
     123    raise (SIGUSR1);
     124    TEST_VERIFY_EXIT (atomic_load (&signal_count) == 2);
     125  #endif
     126  
     127    xfree_sigstack (sstk);
     128    return 0;
     129  }
     130  
     131  #include <support/test-driver.c>