1  // Low-level functions for atomic operations: m68k version -*- C++ -*-
       2  
       3  // Copyright (C) 2001-2023 Free Software Foundation, Inc.
       4  //
       5  // This file is part of the GNU ISO C++ Library.  This library is free
       6  // software; you can redistribute it and/or modify it under the
       7  // terms of the GNU General Public License as published by the
       8  // Free Software Foundation; either version 3, or (at your option)
       9  // any later version.
      10  
      11  // This library is distributed in the hope that it will be useful,
      12  // but WITHOUT ANY WARRANTY; without even the implied warranty of
      13  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      14  // GNU General Public License for 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 <ext/atomicity.h>
      26  
      27  namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
      28  {
      29  _GLIBCXX_BEGIN_NAMESPACE_VERSION
      30  
      31  #if ( defined(__mc68020__) || defined(__mc68030__) \
      32        || defined(__mc68040__) || defined(__mc68060__) ) \
      33      && !defined(__mcpu32__)
      34    // These variants support compare-and-swap.
      35    _Atomic_word
      36    __attribute__ ((__unused__))
      37    __exchange_and_add(volatile _Atomic_word* __mem, int __val) throw ()
      38    {
      39      register _Atomic_word __result = *__mem;
      40      register _Atomic_word __temp;
      41      __asm__ __volatile__ ("1: move%.l %0,%1\n\t"
      42  			  "add%.l %3,%1\n\t"
      43  			  "cas%.l %0,%1,%2\n\t"
      44  			  "jne 1b"
      45  			  : "=d" (__result), "=&d" (__temp), "=m" (*__mem)
      46  			  : "d" (__val), "0" (__result), "m" (*__mem));
      47      return __result;
      48    }
      49  
      50  #elif defined(__rtems__)
      51    // This code is only provided for reference.  RTEMS uses now the atomic
      52    // builtins and libatomic.  See configure.host.
      53    //
      54    // TAS/JBNE is unsafe on systems with strict priority-based scheduling.
      55    // Disable interrupts, which we can do only from supervisor mode.
      56    _Atomic_word
      57    __attribute__ ((__unused__))
      58    __exchange_and_add(volatile _Atomic_word* __mem, int __val) throw ()
      59    {
      60      _Atomic_word __result;
      61      short __level, __tmpsr;
      62      __asm__ __volatile__ ("move%.w %%sr,%0\n\tor%.l %0,%1\n\tmove%.w %1,%%sr"
      63  			  : "=d"(__level), "=d"(__tmpsr) : "1"(0x700));
      64  
      65      __result = *__mem;
      66      *__mem = __result + __val;
      67      __asm__ __volatile__ ("move%.w %0,%%sr" : : "d"(__level));
      68  
      69      return __result;
      70    }
      71  
      72  #else
      73  
      74    template<int __inst>
      75      struct _Atomicity_lock
      76      {
      77        static volatile unsigned char _S_atomicity_lock;
      78      };
      79  
      80    template<int __inst>
      81    volatile unsigned char _Atomicity_lock<__inst>::_S_atomicity_lock = 0;
      82  
      83    template volatile unsigned char _Atomicity_lock<0>::_S_atomicity_lock;
      84  
      85    _Atomic_word
      86    __attribute__ ((__unused__))
      87    __exchange_and_add(volatile _Atomic_word* __mem, int __val) throw ()
      88    {
      89      _Atomic_word __result;
      90  
      91      // bset with no immediate addressing (not SMP-safe)
      92  #if defined(__mcfisaa__) || defined(__mcfisaaplus__)
      93      __asm__ __volatile__("1: bset.b #7,%0@\n\tjbne 1b"
      94  			 : /* no outputs */
      95  			 : "a"(&_Atomicity_lock<0>::_S_atomicity_lock)
      96  			 : "cc", "memory");
      97  
      98      // CPU32 and CF ISAs B & C support test-and-set (SMP-safe).
      99  #elif defined(__mcpu32__) || defined(__mcfisab__) || defined (__mcfisac__)
     100      __asm__ __volatile__("1: tas %0\n\tjbne 1b"
     101  			 : "+m"(_Atomicity_lock<0>::_S_atomicity_lock)
     102  			 : /* none */
     103  			 : "cc");
     104  
     105      // Use bset with immediate addressing for 68000/68010 (not SMP-safe)
     106      // NOTE: TAS is available on the 68000, but unsupported by some Amiga
     107      // memory controllers.
     108  #else
     109      __asm__ __volatile__("1: bset.b #7,%0\n\tjbne 1b"
     110  			 : "+m"(_Atomicity_lock<0>::_S_atomicity_lock)
     111  			 : /* none */
     112  			 : "cc");
     113  #endif
     114  
     115      __result = *__mem;
     116      *__mem = __result + __val;
     117  
     118      _Atomicity_lock<0>::_S_atomicity_lock = 0;
     119  
     120      return __result;
     121    }
     122  
     123  #endif /* TAS / BSET */
     124  
     125    void
     126    __attribute__ ((__unused__))
     127    __atomic_add(volatile _Atomic_word* __mem, int __val) throw ()
     128    {
     129      // Careful: using add.l with a memory destination is not
     130      // architecturally guaranteed to be atomic.
     131      __exchange_and_add(__mem, __val);
     132    }
     133  
     134  _GLIBCXX_END_NAMESPACE_VERSION
     135  } // namespace