/* * Simple interface for atomic operations. * * Copyright (C) 2013 Red Hat, Inc. * * Author: Paolo Bonzini * * This work is licensed under the terms of the GNU GPL, version 2 or later. * See the COPYING file in the top-level directory. * * See docs/atomics.txt for discussion about the guarantees each * atomic primitive is meant to provide. */ #ifndef QEMU_ATOMIC_H #define QEMU_ATOMIC_H /* Compiler barrier */ #define barrier() ({ asm volatile("" ::: "memory"); (void)0; }) /* The variable that receives the old value of an atomically-accessed * variable must be non-qualified, because atomic builtins return values * through a pointer-type argument as in __atomic_load(&var, &old, MODEL). * * This macro has to handle types smaller than int manually, because of * implicit promotion. int and larger types, as well as pointers, can be * converted to a non-qualified type just by applying a binary operator. */ #define typeof_strip_qual(expr) \ typeof( \ __builtin_choose_expr( \ __builtin_types_compatible_p(typeof(expr), bool) || \ __builtin_types_compatible_p(typeof(expr), const bool) || \ __builtin_types_compatible_p(typeof(expr), volatile bool) || \ __builtin_types_compatible_p(typeof(expr), const volatile bool), \ (bool)1, \ __builtin_choose_expr( \ __builtin_types_compatible_p(typeof(expr), signed char) || \ __builtin_types_compatible_p(typeof(expr), const signed char) || \ __builtin_types_compatible_p(typeof(expr), volatile signed char) || \ __builtin_types_compatible_p(typeof(expr), const volatile signed char), \ (signed char)1, \ __builtin_choose_expr( \ __builtin_types_compatible_p(typeof(expr), unsigned char) || \ __builtin_types_compatible_p(typeof(expr), const unsigned char) || \ __builtin_types_compatible_p(typeof(expr), volatile unsigned char) || \ __builtin_types_compatible_p(typeof(expr), const volatile unsigned char), \ (unsigned char)1, \ __builtin_choose_expr( \ __builtin_types_compatible_p(typeof(expr), signed short) || \ __builtin_types_compatible_p(typeof(expr), const signed short) || \ __builtin_types_compatible_p(typeof(expr), volatile signed short) || \ __builtin_types_compatible_p(typeof(expr), const volatile signed short), \ (signed short)1, \ __builtin_choose_expr( \ __builtin_types_compatible_p(typeof(expr), unsigned short) || \ __builtin_types_compatible_p(typeof(expr), const unsigned short) || \ __builtin_types_compatible_p(typeof(expr), volatile unsigned short) || \ __builtin_types_compatible_p(typeof(expr), const volatile unsigned short), \ (unsigned short)1, \ (expr)+0)))))) #ifdef __ATOMIC_RELAXED /* For C11 atomic ops */ /* Manual memory barriers * *__atomic_thread_fence does not include a compiler barrier; instead, * the barrier is part of __atomic_load/__atomic_store's "volatile-like" * semantics. If smp_wmb() is a no-op, absence of the barrier means that * the compiler is free to reorder stores on each side of the barrier. * Add one here, and similarly in smp_rmb() and smp_read_barrier_depends(). */ #define smp_mb() ({ barrier(); __atomic_thread_fence(__ATOMIC_SEQ_CST); }) #define smp_mb_release() ({ barrier(); __atomic_thread_fence(__ATOMIC_RELEASE); }) #define smp_mb_acquire() ({ barrier(); __atomic_thread_fence(__ATOMIC_ACQUIRE); }) /* Most compilers currently treat consume and acquire the same, but really * no processors except Alpha need a barrier here. Leave it in if * using Thread Sanitizer to avoid warnings, otherwise optimize it away. */ #if defined(__SANITIZE_THREAD__) #define smp_read_barrier_depends() ({ barrier(); __atomic_thread_fence(__ATOMIC_CONSUME); }) #elif defined(__alpha__) #define smp_read_barrier_depends() asm volatile("mb":::"memory") #else #define smp_read_barrier_depends() barrier() #endif /* Sanity check that the size of an atomic operation isn't "overly large". * Despite the fact that e.g. i686 has 64-bit atomic operations, we do not * want to use them because we ought not need them, and this lets us do a * bit of sanity checking that other 32-bit hosts might build. * * That said, we have a problem on 64-bit ILP32 hosts in that in order to * sync with TCG_OVERSIZED_GUEST, this must match TCG_TARGET_REG_BITS. * We'd prefer not want to pull in everything else TCG related, so handle * those few cases by hand. * * Note that x32 is fully detected with __x64_64__ + _ILP32, and that for * Sparc we always force the use of sparcv9 in configure. */ #if defined(__x86_64__) || defined(__sparc__) # define ATOMIC_REG_SIZE 8 #else # define ATOMIC_REG_SIZE sizeof(void *) #endif /* Weak atomic operations prevent the compiler moving other * loads/stores past the atomic operation load/store. However there is * no explicit memory barrier for the processor. * * The C11 memory model says that variables that are accessed from * different threads should at least be done with __ATOMIC_RELAXED * primitives or the result is undefined. Generally this has little to * no effect on the generated code but not using the atomic primitives * will get flagged by sanitizers as a violation. */ #define atomic_read__nocheck(ptr) \ __atomic_load_n(ptr, __ATOMIC_RELAXED) #define atomic_read(ptr) \ ({ \ QEMU_BUILD_BUG_ON(sizeof(*ptr) > ATOMIC_REG_SIZE); \ atomic_read__nocheck(ptr); \ }) #define atomic_set__nocheck(ptr, i) \ __atomic_store_n(ptr, i, __ATOMIC_RELAXED) #define atomic_set(ptr, i) do { \ QEMU_BUILD_BUG_ON(sizeof(*ptr) > ATOMIC_REG_SIZE); \ atomic_set__nocheck(ptr, i); \ } while(0) /* See above: most compilers currently treat consume and acquire the * same, but this slows down atomic_rcu_read unnecessarily. */ #ifdef __SANITIZE_THREAD__ #define atomic_rcu_read__nocheck(ptr, valptr) \ __atomic_load(ptr, valptr, __ATOMIC_CONSUME); #else #define atomic_rcu_read__nocheck(ptr, valptr) \ __atomic_load(ptr, valptr, __ATOMIC_RELAXED); \ smp_read_barrier_depends(); #endif #define atomic_rcu_read(ptr) \ ({ \ QEMU_BUILD_BUG_ON(sizeof(*ptr) > ATOMIC_REG_SIZE); \ typeof_strip_qual(*ptr) _val; \ atomic_rcu_read__nocheck(ptr, &_val); \ _val; \ }) #define atomic_rcu_set(ptr, i) do { \ QEMU_BUILD_BUG_ON(sizeof(*ptr) > ATOMIC_REG_SIZE); \ __atomic_store_n(ptr, i, __ATOMIC_RELEASE); \ } while(0) #define atomic_load_acquire(ptr) \ ({ \ QEMU_BUILD_BUG_ON(sizeof(*ptr) > ATOMIC_REG_SIZE); \ typeof_strip_qual(*ptr) _val; \ __atomic_load(ptr, &_val, __ATOMIC_ACQUIRE); \ _val; \ }) #define atomic_store_release(ptr, i) do { \ QEMU_BUILD_BUG_ON(sizeof(*ptr) > ATOMIC_REG_SIZE); \ __atomic_store_n(ptr, i, __ATOMIC_RELEASE); \ } while(0) /* All the remaining operations are fully sequentially consistent */ #define atomic_xchg__nocheck(ptr, i) ({ \ __atomic_exchange_n(ptr, (i), __ATOMIC_SEQ_CST); \ }) #define atomic_xchg(ptr, i) ({ \ QEMU_BUILD_BUG_ON(sizeof(*ptr) > ATOMIC_REG_SIZE); \ atomic_xchg__nocheck(ptr, i); \ }) /* Returns the eventual value, failed or not */ #define atomic_cmpxchg__nocheck(ptr, old, new) ({ \ typeof_strip_qual(*ptr) _old = (old); \ __atomic_compare_exchange_n(ptr, &_old, new, false, \ __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST); \ _old; \ }) #define atomic_cmpxchg(ptr, old, new) ({ \ QEMU_BUILD_BUG_ON(sizeof(*ptr) > ATOMIC_REG_SIZE); \ atomic_cmpxchg__nocheck(ptr, old, new); \ }) /* Provide shorter names for GCC atomic builtins, return old value */ #define atomic_fetch_inc(ptr) __atomic_fetch_add(ptr, 1, __ATOMIC_SEQ_CST) #define atomic_fetch_dec(ptr) __atomic_fetch_sub(ptr, 1, __ATOMIC_SEQ_CST) #define atomic_fetch_add(ptr, n) __atomic_fetch_add(ptr, n, __ATOMIC_SEQ_CST) #define atomic_fetch_sub(ptr, n) __atomic_fetch_sub(ptr, n, __ATOMIC_SEQ_CST) #define atomic_fetch_and(ptr, n) __atomic_fetch_and(ptr, n, __ATOMIC_SEQ_CST) #define atomic_fetch_or(ptr, n) __atomic_fetch_or(ptr, n, __ATOMIC_SEQ_CST) #define atomic_fetch_xor(ptr, n) __atomic_fetch_xor(ptr, n, __ATOMIC_SEQ_CST) #define atomic_inc_fetch(ptr) __atomic_add_fetch(ptr, 1, __ATOMIC_SEQ_CST) #define atomic_dec_fetch(ptr) __atomic_sub_fetch(ptr, 1, __ATOMIC_SEQ_CST) #define atomic_add_fetch(ptr, n) __atomic_add_fetch(ptr, n, __ATOMIC_SEQ_CST) #define atomic_sub_fetch(ptr, n) __atomic_sub_fetch(ptr, n, __ATOMIC_SEQ_CST) #define atomic_and_fetch(ptr, n) __atomic_and_fetch(ptr, n, __ATOMIC_SEQ_CST) #define atomic_or_fetch(ptr, n) __atomic_or_fetch(ptr, n, __ATOMIC_SEQ_CST) #define atomic_xor_fetch(ptr, n) __atomic_xor_fetch(ptr, n, __ATOMIC_SEQ_CST) /* And even shorter names that return void. */ #define atomic_inc(ptr) ((void) __atomic_fetch_add(ptr, 1, __ATOMIC_SEQ_CST)) #define atomic_dec(ptr) ((void) __atomic_fetch_sub(ptr, 1, __ATOMIC_SEQ_CST)) #define atomic_add(ptr, n) ((void) __atomic_fetch_add(ptr, n, __ATOMIC_SEQ_CST)) #define atomic_sub(ptr, n) ((void) __atomic_fetch_sub(ptr, n, __ATOMIC_SEQ_CST)) #define atomic_and(ptr, n) ((void) __atomic_fetch_and(ptr, n, __ATOMIC_SEQ_CST)) #define atomic_or(ptr, n) ((void) __atomic_fetch_or(ptr, n, __ATOMIC_SEQ_CST)) #define atomic_xor(ptr, n) ((void) __atomic_fetch_xor(ptr, n, __ATOMIC_SEQ_CST)) #else /* __ATOMIC_RELAXED */ /* * We use GCC builtin if it's available, as that can use mfence on * 32-bit as well, e.g. if built with -march=pentium-m. However, on * i386 the spec is buggy, and the implementation followed it until * 4.3 (http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36793). */ #if defined(__i386__) || defined(__x86_64__) #if !QEMU_GNUC_PREREQ(4, 4) #if defined __x86_64__ #define smp_mb() ({ asm volatile("mfence" ::: "memory"); (void)0; }) #else #define smp_mb() ({ asm volatile("lock; addl $0,0(%%esp) " ::: "memory"); (void)0; }) #endif #endif #endif #ifdef __alpha__ #define smp_read_barrier_depends() asm volatile("mb":::"memory") #endif #if defined(__i386__) || defined(__x86_64__) || defined(__s390x__) /* * Because of the strongly ordered storage model, wmb() and rmb() are nops * here (a compiler barrier only). QEMU doesn't do accesses to write-combining * qemu memory or non-temporal load/stores from C code. */ #define smp_mb_release() barrier() #define smp_mb_acquire() barrier() /* * __sync_lock_test_and_set() is documented to be an acquire barrier only, * but it is a full barrier at the hardware level. Add a compiler barrier * to make it a full barrier also at the compiler level. */ #define atomic_xchg(ptr, i) (barrier(), __sync_lock_test_and_set(ptr, i)) #elif defined(_ARCH_PPC) /* * We use an eieio() for wmb() on powerpc. This assumes we don't * need to order cacheable and non-cacheable stores with respect to * each other. * * smp_mb has the same problem as on x86 for not-very-new GCC * (http://patchwork.ozlabs.org/patch/126184/, Nov 2011). */ #define smp_wmb() ({ asm volatile("eieio" ::: "memory"); (void)0; }) #if defined(__powerpc64__) #define smp_mb_release() ({ asm volatile("lwsync" ::: "memory"); (void)0; }) #define smp_mb_acquire() ({ asm volatile("lwsync" ::: "memory"); (void)0; }) #else #define smp_mb_release() ({ asm volatile("sync" ::: "memory"); (void)0; }) #define smp_mb_acquire() ({ asm volatile("sync" ::: "memory"); (void)0; }) #endif #define smp_mb() ({ asm volatile("sync" ::: "memory"); (void)0; }) #endif /* _ARCH_PPC */ /* * For (host) platforms we don't have explicit barrier definitions * for, we use the gcc __sync_synchronize() primitive to generate a * full barrier. This should be safe on all platforms, though it may * be overkill for smp_mb_acquire() and smp_mb_release(). */ #ifndef smp_mb #define smp_mb() __sync_synchronize() #endif #ifndef smp_mb_acquire #define smp_mb_acquire() __sync_synchronize() #endif #ifndef smp_mb_release #define smp_mb_release() __sync_synchronize() #endif #ifndef smp_read_barrier_depends #define smp_read_barrier_depends() barrier() #endif /* These will only be atomic if the processor does the fetch or store * in a single issue memory operation */ #define atomic_read__nocheck(p) (*(__typeof__(*(p)) volatile*) (p)) #define atomic_set__nocheck(p, i) ((*(__typeof__(*(p)) volatile*) (p)) = (i)) #define atomic_read(ptr) atomic_read__nocheck(ptr) #define atomic_set(ptr, i) atomic_set__nocheck(ptr,i) /** * atomic_rcu_read - reads a RCU-protected pointer to a local variable * into a RCU read-side critical section. The pointer can later be safely * dereferenced within the critical section. * * This ensures that the pointer copy is invariant thorough the whole critical * section. * * Inserts memory barriers on architectures that require them (currently only * Alpha) and documents which pointers are protected by RCU. * * atomic_rcu_read also includes a compiler barrier to ensure that * value-speculative optimizations (e.g. VSS: Value Speculation * Scheduling) does not perform the data read before the pointer read * by speculating the value of the pointer. * * Should match atomic_rcu_set(), atomic_xchg(), atomic_cmpxchg(). */ #define atomic_rcu_read(ptr) ({ \ typeof(*ptr) _val = atomic_read(ptr); \ smp_read_barrier_depends(); \ _val; \ }) /** * atomic_rcu_set - assigns (publicizes) a pointer to a new data structure * meant to be read by RCU read-side critical sections. * * Documents which pointers will be dereferenced by RCU read-side critical * sections and adds the required memory barriers on architectures requiring * them. It also makes sure the compiler does not reorder code initializing the * data structure before its publication. * * Should match atomic_rcu_read(). */ #define atomic_rcu_set(ptr, i) do { \ smp_wmb(); \ atomic_set(ptr, i); \ } while (0) #define atomic_load_acquire(ptr) ({ \ typeof(*ptr) _val = atomic_read(ptr); \ smp_mb_acquire(); \ _val; \ }) #define atomic_store_release(ptr, i) do { \ smp_mb_release(); \ atomic_set(ptr, i); \ } while (0) #ifndef atomic_xchg #if defined(__clang__) #define atomic_xchg(ptr, i) __sync_swap(ptr, i) #else /* __sync_lock_test_and_set() is documented to be an acquire barrier only. */ #define atomic_xchg(ptr, i) (smp_mb(), __sync_lock_test_and_set(ptr, i)) #endif #endif #define atomic_xchg__nocheck atomic_xchg /* Provide shorter names for GCC atomic builtins. */ #define atomic_fetch_inc(ptr) __sync_fetch_and_add(ptr, 1) #define atomic_fetch_dec(ptr) __sync_fetch_and_add(ptr, -1) #define atomic_fetch_add(ptr, n) __sync_fetch_and_add(ptr, n) #define atomic_fetch_sub(ptr, n) __sync_fetch_and_sub(ptr, n) #define atomic_fetch_and(ptr, n) __sync_fetch_and_and(ptr, n) #define atomic_fetch_or(ptr, n) __sync_fetch_and_or(ptr, n) #define atomic_fetch_xor(ptr, n) __sync_fetch_and_xor(ptr, n) #define atomic_inc_fetch(ptr) __sync_add_and_fetch(ptr, 1) #define atomic_dec_fetch(ptr) __sync_add_and_fetch(ptr, -1) #define atomic_add_fetch(ptr, n) __sync_add_and_fetch(ptr, n) #define atomic_sub_fetch(ptr, n) __sync_sub_and_fetch(ptr, n) #define atomic_and_fetch(ptr, n) __sync_and_and_fetch(ptr, n) #define atomic_or_fetch(ptr, n) __sync_or_and_fetch(ptr, n) #define atomic_xor_fetch(ptr, n) __sync_xor_and_fetch(ptr, n) #define atomic_cmpxchg(ptr, old, new) __sync_val_compare_and_swap(ptr, old, new) #define atomic_cmpxchg__nocheck(ptr, old, new) atomic_cmpxchg(ptr, old, new) /* And even shorter names that return void. */ #define atomic_inc(ptr) ((void) __sync_fetch_and_add(ptr, 1)) #define atomic_dec(ptr) ((void) __sync_fetch_and_add(ptr, -1)) #define atomic_add(ptr, n) ((void) __sync_fetch_and_add(ptr, n)) #define atomic_sub(ptr, n) ((void) __sync_fetch_and_sub(ptr, n)) #define atomic_and(ptr, n) ((void) __sync_fetch_and_and(ptr, n)) #define atomic_or(ptr, n) ((void) __sync_fetch_and_or(ptr, n)) #define atomic_xor(ptr, n) ((void) __sync_fetch_and_xor(ptr, n)) #endif /* __ATOMIC_RELAXED */ #ifndef smp_wmb #define smp_wmb() smp_mb_release() #endif #ifndef smp_rmb #define smp_rmb() smp_mb_acquire() #endif /* This is more efficient than a store plus a fence. */ #if !defined(__SANITIZE_THREAD__) #if defined(__i386__) || defined(__x86_64__) || defined(__s390x__) #define atomic_mb_set(ptr, i) ((void)atomic_xchg(ptr, i)) #endif #endif /* atomic_mb_read/set semantics map Java volatile variables. They are * less expensive on some platforms (notably POWER) than fully * sequentially consistent operations. * * As long as they are used as paired operations they are safe to * use. See docs/atomic.txt for more discussion. */ #ifndef atomic_mb_read #define atomic_mb_read(ptr) \ atomic_load_acquire(ptr) #endif #ifndef atomic_mb_set #define atomic_mb_set(ptr, i) do { \ atomic_store_release(ptr, i); \ smp_mb(); \ } while(0) #endif #endif /* QEMU_ATOMIC_H */