1 /* 2 * Simple interface for atomic operations. 3 * 4 * Copyright (C) 2013 Red Hat, Inc. 5 * 6 * Author: Paolo Bonzini <pbonzini@redhat.com> 7 * 8 * This work is licensed under the terms of the GNU GPL, version 2 or later. 9 * See the COPYING file in the top-level directory. 10 * 11 * See docs/devel/atomics.rst for discussion about the guarantees each 12 * atomic primitive is meant to provide. 13 */ 14 15 #ifndef QEMU_ATOMIC_H 16 #define QEMU_ATOMIC_H 17 18 #include "compiler.h" 19 20 /* Compiler barrier */ 21 #define barrier() ({ asm volatile("" ::: "memory"); (void)0; }) 22 23 #ifndef __ATOMIC_RELAXED 24 #error "Expecting C11 atomic ops" 25 #endif 26 27 /* Manual memory barriers 28 * 29 *__atomic_thread_fence does not include a compiler barrier; instead, 30 * the barrier is part of __atomic_load/__atomic_store's "volatile-like" 31 * semantics. If smp_wmb() is a no-op, absence of the barrier means that 32 * the compiler is free to reorder stores on each side of the barrier. 33 * Add one here, and similarly in smp_rmb() and smp_read_barrier_depends(). 34 */ 35 36 #define smp_mb() ({ barrier(); __atomic_thread_fence(__ATOMIC_SEQ_CST); }) 37 #define smp_mb_release() ({ barrier(); __atomic_thread_fence(__ATOMIC_RELEASE); }) 38 #define smp_mb_acquire() ({ barrier(); __atomic_thread_fence(__ATOMIC_ACQUIRE); }) 39 40 /* Most compilers currently treat consume and acquire the same, but really 41 * no processors except Alpha need a barrier here. Leave it in if 42 * using Thread Sanitizer to avoid warnings, otherwise optimize it away. 43 */ 44 #ifdef QEMU_SANITIZE_THREAD 45 #define smp_read_barrier_depends() ({ barrier(); __atomic_thread_fence(__ATOMIC_CONSUME); }) 46 #elif defined(__alpha__) 47 #define smp_read_barrier_depends() asm volatile("mb":::"memory") 48 #else 49 #define smp_read_barrier_depends() barrier() 50 #endif 51 52 /* 53 * A signal barrier forces all pending local memory ops to be observed before 54 * a SIGSEGV is delivered to the *same* thread. In practice this is exactly 55 * the same as barrier(), but since we have the correct builtin, use it. 56 */ 57 #define signal_barrier() __atomic_signal_fence(__ATOMIC_SEQ_CST) 58 59 /* 60 * Sanity check that the size of an atomic operation isn't "overly large". 61 * Despite the fact that e.g. i686 has 64-bit atomic operations, we do not 62 * want to use them because we ought not need them, and this lets us do a 63 * bit of sanity checking that other 32-bit hosts might build. 64 */ 65 #define ATOMIC_REG_SIZE sizeof(void *) 66 67 /* Weak atomic operations prevent the compiler moving other 68 * loads/stores past the atomic operation load/store. However there is 69 * no explicit memory barrier for the processor. 70 * 71 * The C11 memory model says that variables that are accessed from 72 * different threads should at least be done with __ATOMIC_RELAXED 73 * primitives or the result is undefined. Generally this has little to 74 * no effect on the generated code but not using the atomic primitives 75 * will get flagged by sanitizers as a violation. 76 */ 77 #define qatomic_read__nocheck(ptr) \ 78 __atomic_load_n(ptr, __ATOMIC_RELAXED) 79 80 #define qatomic_read(ptr) \ 81 ({ \ 82 qemu_build_assert(sizeof(*ptr) <= ATOMIC_REG_SIZE); \ 83 qatomic_read__nocheck(ptr); \ 84 }) 85 86 #define qatomic_set__nocheck(ptr, i) \ 87 __atomic_store_n(ptr, i, __ATOMIC_RELAXED) 88 89 #define qatomic_set(ptr, i) do { \ 90 qemu_build_assert(sizeof(*ptr) <= ATOMIC_REG_SIZE); \ 91 qatomic_set__nocheck(ptr, i); \ 92 } while(0) 93 94 /* See above: most compilers currently treat consume and acquire the 95 * same, but this slows down qatomic_rcu_read unnecessarily. 96 */ 97 #ifdef QEMU_SANITIZE_THREAD 98 #define qatomic_rcu_read__nocheck(ptr, valptr) \ 99 __atomic_load(ptr, valptr, __ATOMIC_CONSUME); 100 #else 101 #define qatomic_rcu_read__nocheck(ptr, valptr) \ 102 __atomic_load(ptr, valptr, __ATOMIC_RELAXED); \ 103 smp_read_barrier_depends(); 104 #endif 105 106 /* 107 * Preprocessor sorcery ahead: use a different identifier for the 108 * local variable in each expansion, so we can nest macro calls 109 * without shadowing variables. 110 */ 111 #define qatomic_rcu_read_internal(ptr, _val) \ 112 ({ \ 113 qemu_build_assert(sizeof(*ptr) <= ATOMIC_REG_SIZE); \ 114 typeof_strip_qual(*ptr) _val; \ 115 qatomic_rcu_read__nocheck(ptr, &_val); \ 116 _val; \ 117 }) 118 #define qatomic_rcu_read(ptr) \ 119 qatomic_rcu_read_internal((ptr), MAKE_IDENTIFIER(_val)) 120 121 #define qatomic_rcu_set(ptr, i) do { \ 122 qemu_build_assert(sizeof(*ptr) <= ATOMIC_REG_SIZE); \ 123 __atomic_store_n(ptr, i, __ATOMIC_RELEASE); \ 124 } while(0) 125 126 #define qatomic_load_acquire(ptr) \ 127 ({ \ 128 qemu_build_assert(sizeof(*ptr) <= ATOMIC_REG_SIZE); \ 129 typeof_strip_qual(*ptr) _val; \ 130 __atomic_load(ptr, &_val, __ATOMIC_ACQUIRE); \ 131 _val; \ 132 }) 133 134 #define qatomic_store_release(ptr, i) do { \ 135 qemu_build_assert(sizeof(*ptr) <= ATOMIC_REG_SIZE); \ 136 __atomic_store_n(ptr, i, __ATOMIC_RELEASE); \ 137 } while(0) 138 139 140 /* All the remaining operations are fully sequentially consistent */ 141 142 #define qatomic_xchg__nocheck(ptr, i) ({ \ 143 __atomic_exchange_n(ptr, (i), __ATOMIC_SEQ_CST); \ 144 }) 145 146 #define qatomic_xchg(ptr, i) ({ \ 147 qemu_build_assert(sizeof(*ptr) <= ATOMIC_REG_SIZE); \ 148 qatomic_xchg__nocheck(ptr, i); \ 149 }) 150 151 /* Returns the old value of '*ptr' (whether the cmpxchg failed or not) */ 152 #define qatomic_cmpxchg__nocheck(ptr, old, new) ({ \ 153 typeof_strip_qual(*ptr) _old = (old); \ 154 (void)__atomic_compare_exchange_n(ptr, &_old, new, false, \ 155 __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST); \ 156 _old; \ 157 }) 158 159 #define qatomic_cmpxchg(ptr, old, new) ({ \ 160 qemu_build_assert(sizeof(*ptr) <= ATOMIC_REG_SIZE); \ 161 qatomic_cmpxchg__nocheck(ptr, old, new); \ 162 }) 163 164 /* Provide shorter names for GCC atomic builtins, return old value */ 165 #define qatomic_fetch_inc(ptr) __atomic_fetch_add(ptr, 1, __ATOMIC_SEQ_CST) 166 #define qatomic_fetch_dec(ptr) __atomic_fetch_sub(ptr, 1, __ATOMIC_SEQ_CST) 167 168 #define qatomic_fetch_add(ptr, n) __atomic_fetch_add(ptr, n, __ATOMIC_SEQ_CST) 169 #define qatomic_fetch_sub(ptr, n) __atomic_fetch_sub(ptr, n, __ATOMIC_SEQ_CST) 170 #define qatomic_fetch_and(ptr, n) __atomic_fetch_and(ptr, n, __ATOMIC_SEQ_CST) 171 #define qatomic_fetch_or(ptr, n) __atomic_fetch_or(ptr, n, __ATOMIC_SEQ_CST) 172 #define qatomic_fetch_xor(ptr, n) __atomic_fetch_xor(ptr, n, __ATOMIC_SEQ_CST) 173 174 #define qatomic_inc_fetch(ptr) __atomic_add_fetch(ptr, 1, __ATOMIC_SEQ_CST) 175 #define qatomic_dec_fetch(ptr) __atomic_sub_fetch(ptr, 1, __ATOMIC_SEQ_CST) 176 #define qatomic_add_fetch(ptr, n) __atomic_add_fetch(ptr, n, __ATOMIC_SEQ_CST) 177 #define qatomic_sub_fetch(ptr, n) __atomic_sub_fetch(ptr, n, __ATOMIC_SEQ_CST) 178 #define qatomic_and_fetch(ptr, n) __atomic_and_fetch(ptr, n, __ATOMIC_SEQ_CST) 179 #define qatomic_or_fetch(ptr, n) __atomic_or_fetch(ptr, n, __ATOMIC_SEQ_CST) 180 #define qatomic_xor_fetch(ptr, n) __atomic_xor_fetch(ptr, n, __ATOMIC_SEQ_CST) 181 182 /* And even shorter names that return void. */ 183 #define qatomic_inc(ptr) \ 184 ((void) __atomic_fetch_add(ptr, 1, __ATOMIC_SEQ_CST)) 185 #define qatomic_dec(ptr) \ 186 ((void) __atomic_fetch_sub(ptr, 1, __ATOMIC_SEQ_CST)) 187 #define qatomic_add(ptr, n) \ 188 ((void) __atomic_fetch_add(ptr, n, __ATOMIC_SEQ_CST)) 189 #define qatomic_sub(ptr, n) \ 190 ((void) __atomic_fetch_sub(ptr, n, __ATOMIC_SEQ_CST)) 191 #define qatomic_and(ptr, n) \ 192 ((void) __atomic_fetch_and(ptr, n, __ATOMIC_SEQ_CST)) 193 #define qatomic_or(ptr, n) \ 194 ((void) __atomic_fetch_or(ptr, n, __ATOMIC_SEQ_CST)) 195 #define qatomic_xor(ptr, n) \ 196 ((void) __atomic_fetch_xor(ptr, n, __ATOMIC_SEQ_CST)) 197 198 #define smp_wmb() smp_mb_release() 199 #define smp_rmb() smp_mb_acquire() 200 201 /* 202 * SEQ_CST is weaker than the older __sync_* builtins and Linux 203 * kernel read-modify-write atomics. Provide a macro to obtain 204 * the same semantics. 205 */ 206 #if !defined(QEMU_SANITIZE_THREAD) && \ 207 (defined(__i386__) || defined(__x86_64__) || defined(__s390x__)) 208 # define smp_mb__before_rmw() signal_barrier() 209 # define smp_mb__after_rmw() signal_barrier() 210 #else 211 # define smp_mb__before_rmw() smp_mb() 212 # define smp_mb__after_rmw() smp_mb() 213 #endif 214 215 /* 216 * On some architectures, qatomic_set_mb is more efficient than a store 217 * plus a fence. 218 */ 219 220 #if !defined(QEMU_SANITIZE_THREAD) && \ 221 (defined(__i386__) || defined(__x86_64__) || defined(__s390x__)) 222 # define qatomic_set_mb(ptr, i) \ 223 ({ (void)qatomic_xchg(ptr, i); smp_mb__after_rmw(); }) 224 #else 225 # define qatomic_set_mb(ptr, i) \ 226 ({ qatomic_store_release(ptr, i); smp_mb(); }) 227 #endif 228 229 #define qatomic_fetch_inc_nonzero(ptr) ({ \ 230 typeof_strip_qual(*ptr) _oldn = qatomic_read(ptr); \ 231 while (_oldn && qatomic_cmpxchg(ptr, _oldn, _oldn + 1) != _oldn) { \ 232 _oldn = qatomic_read(ptr); \ 233 } \ 234 _oldn; \ 235 }) 236 237 /* 238 * Abstractions to access atomically (i.e. "once") i64/u64 variables. 239 * 240 * The i386 abi is odd in that by default members are only aligned to 241 * 4 bytes, which means that 8-byte types can wind up mis-aligned. 242 * Clang will then warn about this, and emit a call into libatomic. 243 * 244 * Use of these types in structures when they will be used with atomic 245 * operations can avoid this. 246 */ 247 typedef int64_t aligned_int64_t __attribute__((aligned(8))); 248 typedef uint64_t aligned_uint64_t __attribute__((aligned(8))); 249 250 #ifdef CONFIG_ATOMIC64 251 /* Use __nocheck because sizeof(void *) might be < sizeof(u64) */ 252 #define qatomic_read_i64(P) \ 253 _Generic(*(P), int64_t: qatomic_read__nocheck(P)) 254 #define qatomic_read_u64(P) \ 255 _Generic(*(P), uint64_t: qatomic_read__nocheck(P)) 256 #define qatomic_set_i64(P, V) \ 257 _Generic(*(P), int64_t: qatomic_set__nocheck(P, V)) 258 #define qatomic_set_u64(P, V) \ 259 _Generic(*(P), uint64_t: qatomic_set__nocheck(P, V)) 260 261 static inline void qatomic64_init(void) 262 { 263 } 264 #else /* !CONFIG_ATOMIC64 */ 265 int64_t qatomic_read_i64(const int64_t *ptr); 266 uint64_t qatomic_read_u64(const uint64_t *ptr); 267 void qatomic_set_i64(int64_t *ptr, int64_t val); 268 void qatomic_set_u64(uint64_t *ptr, uint64_t val); 269 void qatomic64_init(void); 270 #endif /* !CONFIG_ATOMIC64 */ 271 272 #endif /* QEMU_ATOMIC_H */ 273