1  /* Copyright (C) 2012-2023 Free Software Foundation, Inc.
       2     Contributed by Richard Henderson <rth@redhat.com>.
       3  
       4     This file is part of the GNU Atomic Library (libatomic).
       5  
       6     Libatomic is free software; you can redistribute it and/or modify it
       7     under the terms of the GNU General Public License as published by
       8     the Free Software Foundation; either version 3 of the License, or
       9     (at your option) any later version.
      10  
      11     Libatomic is distributed in the hope that it will be useful, but WITHOUT ANY
      12     WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
      13     FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
      14     more details.
      15  
      16     Under Section 7 of GPL version 3, you are granted additional
      17     permissions described in the GCC Runtime Library Exception, version
      18     3.1, as published by the Free Software Foundation.
      19  
      20     You should have received a copy of the GNU General Public License and
      21     a copy of the GCC Runtime Library Exception along with this program;
      22     see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
      23     <http://www.gnu.org/licenses/>.  */
      24  
      25  #include "libatomic_i.h"
      26  
      27  
      28  /* If we support the builtin, just use it.  */
      29  #if !DONE && SIZE(HAVE_ATOMIC_LDST)
      30  void
      31  SIZE(libat_store) (UTYPE *mptr, UTYPE newval, int smodel)
      32  {
      33    if (maybe_specialcase_relaxed(smodel))
      34      __atomic_store_n (mptr, newval, __ATOMIC_RELAXED);
      35    else if (maybe_specialcase_acqrel(smodel))
      36      /* Note that ACQ and ACQ_REL are not valid for store.  */
      37      __atomic_store_n (mptr, newval, __ATOMIC_RELEASE);
      38    else
      39      __atomic_store_n (mptr, newval, __ATOMIC_SEQ_CST);
      40  }
      41  
      42  #define DONE 1
      43  #endif /* HAVE_ATOMIC_STORE */
      44  
      45  /* If we have compare-and-swap, use it perform the store.  */
      46  #if !DONE && defined(atomic_compare_exchange_n)
      47  void
      48  SIZE(libat_store) (UTYPE *mptr, UTYPE newval, int smodel)
      49  {
      50    UTYPE oldval;
      51  
      52    pre_barrier (smodel);
      53  
      54    oldval = *mptr;
      55    while (!atomic_compare_exchange_n (mptr, &oldval, newval, true,
      56  				     __ATOMIC_RELAXED, __ATOMIC_RELAXED))
      57      continue;
      58  
      59    post_barrier (smodel);
      60  }
      61  
      62  #define DONE 1
      63  #endif /* atomic_compare_exchange_n */
      64  
      65  
      66  /* If this type is smaller than word-sized, fall back to a word-sized
      67     compare-and-swap loop.  */
      68  #if !DONE && N < WORDSIZE && defined(atomic_compare_exchange_w)
      69  void
      70  SIZE(libat_store) (UTYPE *mptr, UTYPE newval, int smodel)
      71  {
      72    UWORD mask, shift, woldval, wnewval, t, *wptr;
      73  
      74    pre_barrier (smodel);
      75  
      76    wptr = (UWORD *)((uintptr_t)mptr & -WORDSIZE);
      77    shift = (((uintptr_t)mptr % WORDSIZE) * CHAR_BIT) ^ SIZE(INVERT_MASK);
      78    mask = SIZE(MASK) << shift;
      79  
      80    wnewval = (UWORD)newval << shift;
      81    woldval = __atomic_load_n (wptr, __ATOMIC_RELAXED);
      82    do
      83      {
      84        t = (woldval & ~mask) | wnewval;
      85      }
      86    while (!atomic_compare_exchange_w (wptr, &woldval, t));
      87  
      88    post_barrier (smodel);
      89  }
      90  
      91  #define DONE 1
      92  #endif /* N < WORDSIZE && atomic_compare_exchange_w */
      93  
      94  
      95  /* Otherwise, fall back to some sort of protection mechanism.  */
      96  #if !DONE
      97  void
      98  SIZE(libat_store) (UTYPE *mptr, UTYPE newval, int smodel)
      99  {
     100    UWORD magic;
     101  
     102    pre_seq_barrier (smodel);
     103    magic = protect_start (mptr);
     104  
     105    *mptr = newval;
     106  
     107    protect_end (mptr, magic);
     108    post_seq_barrier (smodel);
     109  }
     110  #endif
     111  
     112  EXPORT_ALIAS (SIZE(store));