1  /* Copyright (C) 2008-2023 Free Software Foundation, Inc.
       2     Contributed by Jakub Jelinek <jakub@redhat.com>.
       3  
       4     This file is part of the GNU Offloading and Multi Processing Library
       5     (libgomp).
       6  
       7     Libgomp is free software; you can redistribute it and/or modify it
       8     under the terms of the GNU General Public License as published by
       9     the Free Software Foundation; either version 3, or (at your option)
      10     any later version.
      11  
      12     Libgomp is distributed in the hope that it will be useful, but WITHOUT ANY
      13     WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
      14     FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
      15     more details.
      16  
      17     Under Section 7 of GPL version 3, you are granted additional
      18     permissions described in the GCC Runtime Library Exception, version
      19     3.1, as published by the Free Software Foundation.
      20  
      21     You should have received a copy of the GNU General Public License and
      22     a copy of the GCC Runtime Library Exception along with this program;
      23     see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
      24     <http://www.gnu.org/licenses/>.  */
      25  
      26  /* This is a Linux specific implementation of a mutex synchronization
      27     mechanism for libgomp.  This type is private to the library.  This
      28     implementation uses atomic instructions and the futex syscall.  */
      29  
      30  #include <endian.h>
      31  #include <limits.h>
      32  #include "wait.h"
      33  
      34  void *
      35  gomp_ptrlock_get_slow (gomp_ptrlock_t *ptrlock)
      36  {
      37    int *intptr;
      38    uintptr_t oldval = 1;
      39  
      40    __atomic_compare_exchange_n (ptrlock, &oldval, 2, false,
      41  			       MEMMODEL_RELAXED, MEMMODEL_RELAXED);
      42  
      43    /* futex works on ints, not pointers.
      44       But a valid work share pointer will be at least
      45       8 byte aligned, so it is safe to assume the low
      46       32-bits of the pointer won't contain values 1 or 2.  */
      47    __asm volatile ("" : "=r" (intptr) : "0" (ptrlock));
      48  #if __BYTE_ORDER == __BIG_ENDIAN
      49    if (sizeof (*ptrlock) > sizeof (int))
      50      intptr += (sizeof (*ptrlock) / sizeof (int)) - 1;
      51  #endif
      52    do
      53      do_wait (intptr, 2);
      54    while (__atomic_load_n (intptr, MEMMODEL_RELAXED) == 2);
      55    __asm volatile ("" : : : "memory");
      56    return (void *) __atomic_load_n (ptrlock, MEMMODEL_ACQUIRE);
      57  }
      58  
      59  void
      60  gomp_ptrlock_set_slow (gomp_ptrlock_t *ptrlock)
      61  {
      62    int *intptr;
      63  
      64    __asm volatile ("" : "=r" (intptr) : "0" (ptrlock));
      65  #if __BYTE_ORDER == __BIG_ENDIAN
      66    if (sizeof (*ptrlock) > sizeof (int))
      67      intptr += (sizeof (*ptrlock) / sizeof (int)) - 1;
      68  #endif
      69    futex_wake (intptr, INT_MAX);
      70  }