From 3abcdbd14d1b9291f06a4a4bbca313fcfbe5452b Mon Sep 17 00:00:00 2001 From: Mathieu Desnoyers Date: Mon, 19 Apr 2021 11:21:52 -0400 Subject: [PATCH] Fix: use __atomic_load() rather than atomic load explicit Use __atomic_load (gcc extension) rather than atomic load explict (C11/C++11) for rcu_dereference because it does not require the input type to be _Atomic. This fixes a regression with clang introduced by commit 380f4b19052 ("Fix: use atomic load memory_order_consume for rcu_dereference on C11/C++11"). Note that the cmm_smp_read_barrier_depends is removed when using __ATOMIC_CONSUME because their memory ordering effect is redundant. Signed-off-by: Mathieu Desnoyers Change-Id: Icd5f6040e0bd2167844a8d856ae5475ceef17123 --- include/urcu/static/pointer.h | 46 ++++++++++++++++------------------- 1 file changed, 21 insertions(+), 25 deletions(-) diff --git a/include/urcu/static/pointer.h b/include/urcu/static/pointer.h index 891daed..ca9a2f9 100644 --- a/include/urcu/static/pointer.h +++ b/include/urcu/static/pointer.h @@ -61,6 +61,10 @@ extern "C" { * optimizations are taken care of by the "memory_order_consume" atomic * load. * + * Use the gcc __atomic_load() rather than C11/C++11 atomic load + * explicit because the pointer used as input argument is a pointer, + * not an _Atomic type as required by C11/C++11. + * * By defining URCU_DEREFERENCE_USE_VOLATILE, the user requires use of * volatile access to implement rcu_dereference rather than * memory_order_consume load from the C11/C++11 standards. @@ -80,33 +84,25 @@ extern "C" { * expanded directly in non-LGPL code. */ -#ifdef URCU_DEREFERENCE_USE_VOLATILE -# define __rcu_dereference(p) CMM_LOAD_SHARED(p) -#else -# if defined (__cplusplus) -# if __cplusplus >= 201103L -# include -# define __rcu_dereference(p) ((std::atomic<__typeof__(p)>)(p)).load(std::memory_order_consume) -# else -# define __rcu_dereference(p) CMM_LOAD_SHARED(x) -# endif -# else -# if (defined (__STDC_VERSION__) && __STDC_VERSION__ >= 201112L) -# include -# define __rcu_dereference(p) atomic_load_explicit(&(p), memory_order_consume) -# else -# define __rcu_dereference(p) CMM_LOAD_SHARED(p) -# endif -# endif +#if !defined (URCU_DEREFERENCE_USE_VOLATILE) && \ + ((defined (__cplusplus) && __cplusplus >= 201103L) || \ + (defined (__STDC_VERSION__) && __STDC_VERSION__ >= 201112L)) +# define __URCU_DEREFERENCE_USE_ATOMIC_CONSUME #endif -#define _rcu_dereference(p) \ - __extension__ \ - ({ \ - __typeof__(p) _________p1 = __rcu_dereference(p); \ - cmm_smp_read_barrier_depends(); \ - (_________p1); \ - }) +#ifdef __URCU_DEREFERENCE_USE_ATOMIC_CONSUME +# define _rcu_dereference(p) __extension__ ({ \ + __typeof__(p) _________p1; \ + __atomic_load(&(p), &_________p1, __ATOMIC_CONSUME); \ + (_________p1); \ + }) +#else +# define _rcu_dereference(p) __extension__ ({ \ + __typeof__(p) _________p1 = CMM_LOAD_SHARED(p); \ + cmm_smp_read_barrier_depends(); \ + (_________p1); \ + }) +#endif /** * _rcu_cmpxchg_pointer - same as rcu_assign_pointer, but tests if the pointer -- 2.34.1