Chris@102: /*
Chris@102:  * Distributed under the Boost Software License, Version 1.0.
Chris@102:  * (See accompanying file LICENSE_1_0.txt or copy at
Chris@102:  * http://www.boost.org/LICENSE_1_0.txt)
Chris@102:  *
Chris@102:  * Copyright (c) 2009, 2011 Helge Bahmann
Chris@102:  * Copyright (c) 2009 Phil Endecott
Chris@102:  * Copyright (c) 2013 Tim Blechmann
Chris@102:  * Linux-specific code by Phil Endecott
Chris@102:  * Copyright (c) 2014 Andrey Semashev
Chris@102:  */
Chris@102: /*!
Chris@102:  * \file   atomic/detail/ops_linux_arm.hpp
Chris@102:  *
Chris@102:  * This header contains implementation of the \c operations template.
Chris@102:  */
Chris@102: 
Chris@102: #ifndef BOOST_ATOMIC_DETAIL_OPS_LINUX_ARM_HPP_INCLUDED_
Chris@102: #define BOOST_ATOMIC_DETAIL_OPS_LINUX_ARM_HPP_INCLUDED_
Chris@102: 
Chris@102: #include <boost/memory_order.hpp>
Chris@102: #include <boost/atomic/detail/config.hpp>
Chris@102: #include <boost/atomic/detail/storage_type.hpp>
Chris@102: #include <boost/atomic/detail/operations_fwd.hpp>
Chris@102: #include <boost/atomic/capabilities.hpp>
Chris@102: #include <boost/atomic/detail/ops_cas_based.hpp>
Chris@102: #include <boost/atomic/detail/ops_extending_cas_based.hpp>
Chris@102: 
Chris@102: #ifdef BOOST_HAS_PRAGMA_ONCE
Chris@102: #pragma once
Chris@102: #endif
Chris@102: 
Chris@102: namespace boost {
Chris@102: namespace atomics {
Chris@102: namespace detail {
Chris@102: 
Chris@102: // Different ARM processors have different atomic instructions.  In particular,
Chris@102: // architecture versions before v6 (which are still in widespread use, e.g. the
Chris@102: // Intel/Marvell XScale chips like the one in the NSLU2) have only atomic swap.
Chris@102: // On Linux the kernel provides some support that lets us abstract away from
Chris@102: // these differences: it provides emulated CAS and barrier functions at special
Chris@102: // addresses that are guaranteed not to be interrupted by the kernel.  Using
Chris@102: // this facility is slightly slower than inline assembler would be, but much
Chris@102: // faster than a system call.
Chris@102: //
Chris@102: // While this emulated CAS is "strong" in the sense that it does not fail
Chris@102: // "spuriously" (i.e.: it never fails to perform the exchange when the value
Chris@102: // found equals the value expected), it does not return the found value on
Chris@102: // failure. To satisfy the atomic API, compare_exchange_{weak|strong} must
Chris@102: // return the found value on failure, and we have to manually load this value
Chris@102: // after the emulated CAS reports failure. This in turn introduces a race
Chris@102: // between the CAS failing (due to the "wrong" value being found) and subsequently
Chris@102: // loading (which might turn up the "right" value). From an application's
Chris@102: // point of view this looks like "spurious failure", and therefore the
Chris@102: // emulated CAS is only good enough to provide compare_exchange_weak
Chris@102: // semantics.
Chris@102: 
Chris@102: struct linux_arm_cas_base
Chris@102: {
Chris@102:     static BOOST_FORCEINLINE void fence_before_store(memory_order order) BOOST_NOEXCEPT
Chris@102:     {
Chris@102:         if ((order & memory_order_release) != 0)
Chris@102:             hardware_full_fence();
Chris@102:     }
Chris@102: 
Chris@102:     static BOOST_FORCEINLINE void fence_after_store(memory_order order) BOOST_NOEXCEPT
Chris@102:     {
Chris@102:         if (order == memory_order_seq_cst)
Chris@102:             hardware_full_fence();
Chris@102:     }
Chris@102: 
Chris@102:     static BOOST_FORCEINLINE void fence_after_load(memory_order order) BOOST_NOEXCEPT
Chris@102:     {
Chris@102:         if ((order & (memory_order_consume | memory_order_acquire)) != 0)
Chris@102:             hardware_full_fence();
Chris@102:     }
Chris@102: 
Chris@102:     static BOOST_FORCEINLINE void hardware_full_fence() BOOST_NOEXCEPT
Chris@102:     {
Chris@102:         typedef void (*kernel_dmb_t)(void);
Chris@102:         ((kernel_dmb_t)0xffff0fa0)();
Chris@102:     }
Chris@102: };
Chris@102: 
Chris@102: template< bool Signed >
Chris@102: struct linux_arm_cas :
Chris@102:     public linux_arm_cas_base
Chris@102: {
Chris@102:     typedef typename make_storage_type< 4u, Signed >::type storage_type;
Chris@102: 
Chris@102:     static BOOST_FORCEINLINE void store(storage_type volatile& storage, storage_type v, memory_order order) BOOST_NOEXCEPT
Chris@102:     {
Chris@102:         fence_before_store(order);
Chris@102:         storage = v;
Chris@102:         fence_after_store(order);
Chris@102:     }
Chris@102: 
Chris@102:     static BOOST_FORCEINLINE storage_type load(storage_type const volatile& storage, memory_order order) BOOST_NOEXCEPT
Chris@102:     {
Chris@102:         storage_type v = storage;
Chris@102:         fence_after_load(order);
Chris@102:         return v;
Chris@102:     }
Chris@102: 
Chris@102:     static BOOST_FORCEINLINE bool compare_exchange_strong(
Chris@102:         storage_type volatile& storage, storage_type& expected, storage_type desired, memory_order success_order, memory_order failure_order) BOOST_NOEXCEPT
Chris@102:     {
Chris@102:         while (true)
Chris@102:         {
Chris@102:             storage_type tmp = expected;
Chris@102:             if (compare_exchange_weak(storage, tmp, desired, success_order, failure_order))
Chris@102:                 return true;
Chris@102:             if (tmp != expected)
Chris@102:             {
Chris@102:                 expected = tmp;
Chris@102:                 return false;
Chris@102:             }
Chris@102:         }
Chris@102:     }
Chris@102: 
Chris@102:     static BOOST_FORCEINLINE bool compare_exchange_weak(
Chris@102:         storage_type volatile& storage, storage_type& expected, storage_type desired, memory_order, memory_order) BOOST_NOEXCEPT
Chris@102:     {
Chris@102:         typedef storage_type (*kernel_cmpxchg32_t)(storage_type oldval, storage_type newval, volatile storage_type* ptr);
Chris@102: 
Chris@102:         if (((kernel_cmpxchg32_t)0xffff0fc0)(expected, desired, &storage) == 0)
Chris@102:         {
Chris@102:             return true;
Chris@102:         }
Chris@102:         else
Chris@102:         {
Chris@102:             expected = storage;
Chris@102:             return false;
Chris@102:         }
Chris@102:     }
Chris@102: 
Chris@102:     static BOOST_FORCEINLINE bool is_lock_free(storage_type const volatile&) BOOST_NOEXCEPT
Chris@102:     {
Chris@102:         return true;
Chris@102:     }
Chris@102: };
Chris@102: 
Chris@102: template< bool Signed >
Chris@102: struct operations< 1u, Signed > :
Chris@102:     public extending_cas_based_operations< cas_based_operations< linux_arm_cas< Signed > >, 1u, Signed >
Chris@102: {
Chris@102: };
Chris@102: 
Chris@102: template< bool Signed >
Chris@102: struct operations< 2u, Signed > :
Chris@102:     public extending_cas_based_operations< cas_based_operations< linux_arm_cas< Signed > >, 2u, Signed >
Chris@102: {
Chris@102: };
Chris@102: 
Chris@102: template< bool Signed >
Chris@102: struct operations< 4u, Signed > :
Chris@102:     public cas_based_operations< linux_arm_cas< Signed > >
Chris@102: {
Chris@102: };
Chris@102: 
Chris@102: BOOST_FORCEINLINE void thread_fence(memory_order order) BOOST_NOEXCEPT
Chris@102: {
Chris@102:     if (order != memory_order_relaxed)
Chris@102:         linux_arm_cas_base::hardware_full_fence();
Chris@102: }
Chris@102: 
Chris@102: BOOST_FORCEINLINE void signal_fence(memory_order order) BOOST_NOEXCEPT
Chris@102: {
Chris@102:     if (order != memory_order_relaxed)
Chris@102:         __asm__ __volatile__ ("" ::: "memory");
Chris@102: }
Chris@102: 
Chris@102: } // namespace detail
Chris@102: } // namespace atomics
Chris@102: } // namespace boost
Chris@102: 
Chris@102: #endif // BOOST_ATOMIC_DETAIL_OPS_LINUX_ARM_HPP_INCLUDED_