atomicity.h

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// Low-level functions for atomic operations: m68k version -*- C++ -*-

// Copyright (C) 2001, 2002, 2003, 2004 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 2, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License along
// with this library; see the file COPYING.  If not, write to the Free
// Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
// USA.

// As a special exception, you may use this file as part of a free software
// library without restriction.  Specifically, if other files instantiate
// templates or use macros or inline functions from this file, or you compile
// this file and link it with other files to produce an executable, this
// file does not by itself cause the resulting executable to be covered by
// the GNU General Public License.  This exception does not however
// invalidate any other reasons why the executable file might be covered by
// the GNU General Public License.

#include <bits/atomicity.h>

namespace __gnu_cxx
{
#if ( defined(__mc68020__) || defined(__mc68030__) \
      || defined(__mc68040__) || defined(__mc68060__) ) \
    && !defined(__mcpu32__)
  // These variants support compare-and-swap.
  _Atomic_word 
  __attribute__ ((__unused__))
  __exchange_and_add(volatile _Atomic_word* __mem, int __val)
  {
    register _Atomic_word __result = *__mem;
    register _Atomic_word __temp;
    __asm__ __volatile__ ("1: move%.l %0,%1\n\t"
			  "add%.l %3,%1\n\t"
			  "cas%.l %0,%1,%2\n\t"
			  "jne 1b"
			  : "=d" (__result), "=&d" (__temp), "=m" (*__mem)
			  : "d" (__val), "0" (__result), "m" (*__mem));
    return __result;
  }

#elif defined(__rtems__)
  // TAS/JBNE is unsafe on systems with strict priority-based scheduling.
  // Disable interrupts, which we can do only from supervisor mode.
  _Atomic_word
  __attribute__ ((__unused__))
  __exchange_and_add(volatile _Atomic_word* __mem, int __val)
  {
    _Atomic_word __result;
    short __level, __tmpsr;
    __asm__ __volatile__ ("move%.w %%sr,%0\n\tor%.l %0,%1\n\tmove%.w %1,%%sr"
			  : "=d"(__level), "=d"(__tmpsr) : "1"(0x700));
    
    __result = *__mem;
    *__mem = __result + __val;    
    __asm__ __volatile__ ("move%.w %0,%%sr" : : "d"(__level));
    
    return __result;
  }

#else
  
  template<int __inst>
    struct _Atomicity_lock
    {
      static volatile unsigned char _S_atomicity_lock;
    };

  template<int __inst>
  volatile unsigned char _Atomicity_lock<__inst>::_S_atomicity_lock = 0;
  
  template volatile unsigned char _Atomicity_lock<0>::_S_atomicity_lock;
  
  _Atomic_word 
  __attribute__ ((__unused__))
  __exchange_and_add(volatile _Atomic_word* __mem, int __val)
  {
    _Atomic_word __result;
    
    // bset with no immediate addressing (not SMP-safe)
#if defined(__mcf5200__) || defined(__mcf5300__)
    __asm__ __volatile__("1: bset.b #7,%0@\n\tjbne 1b"
			 : /* no outputs */
			 : "a"(&_Atomicity_lock<0>::_S_atomicity_lock)
			 : "cc", "memory");
    
    // CPU32 and MCF5400 support test-and-set (SMP-safe).
#elif defined(__mcpu32__) || defined(__mcf5400__)
    __asm__ __volatile__("1: tas %0\n\tjbne 1b"
			 : "+m"(_Atomicity_lock<0>::_S_atomicity_lock)
			 : /* none */
			 : "cc");
    
    // Use bset with immediate addressing for 68000/68010 (not SMP-safe)
    // NOTE: TAS is available on the 68000, but unsupported by some Amiga
    // memory controllers.
#else
    __asm__ __volatile__("1: bset.b #7,%0\n\tjbne 1b"
			 : "+m"(_Atomicity_lock<0>::_S_atomicity_lock)
			 : /* none */
			 : "cc");
#endif
    
    __result = *__mem;
    *__mem = __result + __val;
    
    _Atomicity_lock<0>::_S_atomicity_lock = 0;
    
    return __result;
  }
  
#endif /* TAS / BSET */

  void
  __attribute__ ((__unused__))
  __atomic_add(volatile _Atomic_word* __mem, int __val)
  {
    // Careful: using add.l with a memory destination is not
    // architecturally guaranteed to be atomic.
    __exchange_and_add(__mem, __val);
  }
} // namespace __gnu_cxx