| /* |
| * Distributed under the Boost Software License, Version 1.0. |
| * (See accompanying file LICENSE_1_0.txt or copy at |
| * http://www.boost.org/LICENSE_1_0.txt) |
| * |
| * Copyright (c) 2009, 2011 Helge Bahmann |
| * Copyright (c) 2009 Phil Endecott |
| * Copyright (c) 2013 Tim Blechmann |
| * Linux-specific code by Phil Endecott |
| * Copyright (c) 2014 Andrey Semashev |
| */ |
| /*! |
| * \file atomic/detail/core_ops_linux_arm.hpp |
| * |
| * This header contains implementation of the \c core_operations template. |
| */ |
| |
| #ifndef BOOST_ATOMIC_DETAIL_CORE_OPS_LINUX_ARM_HPP_INCLUDED_ |
| #define BOOST_ATOMIC_DETAIL_CORE_OPS_LINUX_ARM_HPP_INCLUDED_ |
| |
| #include <cstddef> |
| #include <boost/memory_order.hpp> |
| #include <boost/atomic/detail/config.hpp> |
| #include <boost/atomic/detail/storage_traits.hpp> |
| #include <boost/atomic/detail/core_operations_fwd.hpp> |
| #include <boost/atomic/detail/core_ops_cas_based.hpp> |
| #include <boost/atomic/detail/cas_based_exchange.hpp> |
| #include <boost/atomic/detail/extending_cas_based_arithmetic.hpp> |
| #include <boost/atomic/detail/fence_operations.hpp> |
| #include <boost/atomic/detail/header.hpp> |
| |
| #ifdef BOOST_HAS_PRAGMA_ONCE |
| #pragma once |
| #endif |
| |
| namespace boost { |
| namespace atomics { |
| namespace detail { |
| |
| // Different ARM processors have different atomic instructions. In particular, |
| // architecture versions before v6 (which are still in widespread use, e.g. the |
| // Intel/Marvell XScale chips like the one in the NSLU2) have only atomic swap. |
| // On Linux the kernel provides some support that lets us abstract away from |
| // these differences: it provides emulated CAS and barrier functions at special |
| // addresses that are guaranteed not to be interrupted by the kernel. Using |
| // this facility is slightly slower than inline assembler would be, but much |
| // faster than a system call. |
| // |
| // https://lwn.net/Articles/314561/ |
| // |
| // While this emulated CAS is "strong" in the sense that it does not fail |
| // "spuriously" (i.e.: it never fails to perform the exchange when the value |
| // found equals the value expected), it does not return the found value on |
| // failure. To satisfy the atomic API, compare_exchange_{weak|strong} must |
| // return the found value on failure, and we have to manually load this value |
| // after the emulated CAS reports failure. This in turn introduces a race |
| // between the CAS failing (due to the "wrong" value being found) and subsequently |
| // loading (which might turn up the "right" value). From an application's |
| // point of view this looks like "spurious failure", and therefore the |
| // emulated CAS is only good enough to provide compare_exchange_weak |
| // semantics. |
| |
| struct linux_arm_cas_base |
| { |
| static BOOST_CONSTEXPR_OR_CONST bool full_cas_based = true; |
| static BOOST_CONSTEXPR_OR_CONST bool is_always_lock_free = true; |
| |
| static BOOST_FORCEINLINE void fence_before_store(memory_order order) BOOST_NOEXCEPT |
| { |
| if ((static_cast< unsigned int >(order) & static_cast< unsigned int >(memory_order_release)) != 0u) |
| fence_operations::hardware_full_fence(); |
| } |
| |
| static BOOST_FORCEINLINE void fence_after_store(memory_order order) BOOST_NOEXCEPT |
| { |
| if (order == memory_order_seq_cst) |
| fence_operations::hardware_full_fence(); |
| } |
| |
| static BOOST_FORCEINLINE void fence_after_load(memory_order order) BOOST_NOEXCEPT |
| { |
| if ((static_cast< unsigned int >(order) & (static_cast< unsigned int >(memory_order_consume) | static_cast< unsigned int >(memory_order_acquire))) != 0u) |
| fence_operations::hardware_full_fence(); |
| } |
| }; |
| |
| template< bool Signed, bool Interprocess > |
| struct linux_arm_cas : |
| public linux_arm_cas_base |
| { |
| typedef typename storage_traits< 4u >::type storage_type; |
| |
| static BOOST_CONSTEXPR_OR_CONST std::size_t storage_size = 4u; |
| static BOOST_CONSTEXPR_OR_CONST std::size_t storage_alignment = 4u; |
| static BOOST_CONSTEXPR_OR_CONST bool is_signed = Signed; |
| static BOOST_CONSTEXPR_OR_CONST bool is_interprocess = Interprocess; |
| |
| static BOOST_FORCEINLINE void store(storage_type volatile& storage, storage_type v, memory_order order) BOOST_NOEXCEPT |
| { |
| fence_before_store(order); |
| storage = v; |
| fence_after_store(order); |
| } |
| |
| static BOOST_FORCEINLINE storage_type load(storage_type const volatile& storage, memory_order order) BOOST_NOEXCEPT |
| { |
| storage_type v = storage; |
| fence_after_load(order); |
| return v; |
| } |
| |
| static BOOST_FORCEINLINE bool compare_exchange_strong( |
| storage_type volatile& storage, storage_type& expected, storage_type desired, memory_order success_order, memory_order failure_order) BOOST_NOEXCEPT |
| { |
| while (true) |
| { |
| storage_type tmp = expected; |
| if (compare_exchange_weak(storage, tmp, desired, success_order, failure_order)) |
| return true; |
| if (tmp != expected) |
| { |
| expected = tmp; |
| return false; |
| } |
| } |
| } |
| |
| static BOOST_FORCEINLINE bool compare_exchange_weak( |
| storage_type volatile& storage, storage_type& expected, storage_type desired, memory_order, memory_order) BOOST_NOEXCEPT |
| { |
| typedef storage_type (*kernel_cmpxchg32_t)(storage_type oldval, storage_type newval, volatile storage_type* ptr); |
| |
| if (((kernel_cmpxchg32_t)0xffff0fc0)(expected, desired, &storage) == 0) |
| { |
| return true; |
| } |
| else |
| { |
| expected = storage; |
| return false; |
| } |
| } |
| }; |
| |
| template< bool Signed, bool Interprocess > |
| struct core_operations< 1u, Signed, Interprocess > : |
| public extending_cas_based_arithmetic< core_operations_cas_based< cas_based_exchange< linux_arm_cas< Signed, Interprocess > > >, 1u, Signed > |
| { |
| }; |
| |
| template< bool Signed, bool Interprocess > |
| struct core_operations< 2u, Signed, Interprocess > : |
| public extending_cas_based_arithmetic< core_operations_cas_based< cas_based_exchange< linux_arm_cas< Signed, Interprocess > > >, 2u, Signed > |
| { |
| }; |
| |
| template< bool Signed, bool Interprocess > |
| struct core_operations< 4u, Signed, Interprocess > : |
| public core_operations_cas_based< cas_based_exchange< linux_arm_cas< Signed, Interprocess > > > |
| { |
| }; |
| |
| } // namespace detail |
| } // namespace atomics |
| } // namespace boost |
| |
| #include <boost/atomic/detail/footer.hpp> |
| |
| #endif // BOOST_ATOMIC_DETAIL_CORE_OPS_LINUX_ARM_HPP_INCLUDED_ |