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 /* Compiler barrier */ 19 #define barrier() ({ asm volatile("" ::: "memory"); (void)0; }) 20 21 /* The variable that receives the old value of an atomically-accessed 22 * variable must be non-qualified, because atomic builtins return values 23 * through a pointer-type argument as in __atomic_load(&var, &old, MODEL). 24 * 25 * This macro has to handle types smaller than int manually, because of 26 * implicit promotion. int and larger types, as well as pointers, can be 27 * converted to a non-qualified type just by applying a binary operator. 28 */ 29 #define typeof_strip_qual(expr) \ 30 typeof( \ 31 __builtin_choose_expr( \ 32 __builtin_types_compatible_p(typeof(expr), bool) || \ 33 __builtin_types_compatible_p(typeof(expr), const bool) || \ 34 __builtin_types_compatible_p(typeof(expr), volatile bool) || \ 35 __builtin_types_compatible_p(typeof(expr), const volatile bool), \ 36 (bool)1, \ 37 __builtin_choose_expr( \ 38 __builtin_types_compatible_p(typeof(expr), signed char) || \ 39 __builtin_types_compatible_p(typeof(expr), const signed char) || \ 40 __builtin_types_compatible_p(typeof(expr), volatile signed char) || \ 41 __builtin_types_compatible_p(typeof(expr), const volatile signed char), \ 42 (signed char)1, \ 43 __builtin_choose_expr( \ 44 __builtin_types_compatible_p(typeof(expr), unsigned char) || \ 45 __builtin_types_compatible_p(typeof(expr), const unsigned char) || \ 46 __builtin_types_compatible_p(typeof(expr), volatile unsigned char) || \ 47 __builtin_types_compatible_p(typeof(expr), const volatile unsigned char), \ 48 (unsigned char)1, \ 49 __builtin_choose_expr( \ 50 __builtin_types_compatible_p(typeof(expr), signed short) || \ 51 __builtin_types_compatible_p(typeof(expr), const signed short) || \ 52 __builtin_types_compatible_p(typeof(expr), volatile signed short) || \ 53 __builtin_types_compatible_p(typeof(expr), const volatile signed short), \ 54 (signed short)1, \ 55 __builtin_choose_expr( \ 56 __builtin_types_compatible_p(typeof(expr), unsigned short) || \ 57 __builtin_types_compatible_p(typeof(expr), const unsigned short) || \ 58 __builtin_types_compatible_p(typeof(expr), volatile unsigned short) || \ 59 __builtin_types_compatible_p(typeof(expr), const volatile unsigned short), \ 60 (unsigned short)1, \ 61 (expr)+0)))))) 62 63 #ifndef __ATOMIC_RELAXED 64 #error "Expecting C11 atomic ops" 65 #endif 66 67 /* Manual memory barriers 68 * 69 *__atomic_thread_fence does not include a compiler barrier; instead, 70 * the barrier is part of __atomic_load/__atomic_store's "volatile-like" 71 * semantics. If smp_wmb() is a no-op, absence of the barrier means that 72 * the compiler is free to reorder stores on each side of the barrier. 73 * Add one here, and similarly in smp_rmb() and smp_read_barrier_depends(). 74 */ 75 76 #define smp_mb() ({ barrier(); __atomic_thread_fence(__ATOMIC_SEQ_CST); }) 77 #define smp_mb_release() ({ barrier(); __atomic_thread_fence(__ATOMIC_RELEASE); }) 78 #define smp_mb_acquire() ({ barrier(); __atomic_thread_fence(__ATOMIC_ACQUIRE); }) 79 80 /* Most compilers currently treat consume and acquire the same, but really 81 * no processors except Alpha need a barrier here. Leave it in if 82 * using Thread Sanitizer to avoid warnings, otherwise optimize it away. 83 */ 84 #if defined(__SANITIZE_THREAD__) 85 #define smp_read_barrier_depends() ({ barrier(); __atomic_thread_fence(__ATOMIC_CONSUME); }) 86 #elif defined(__alpha__) 87 #define smp_read_barrier_depends() asm volatile("mb":::"memory") 88 #else 89 #define smp_read_barrier_depends() barrier() 90 #endif 91 92 /* 93 * A signal barrier forces all pending local memory ops to be observed before 94 * a SIGSEGV is delivered to the *same* thread. In practice this is exactly 95 * the same as barrier(), but since we have the correct builtin, use it. 96 */ 97 #define signal_barrier() __atomic_signal_fence(__ATOMIC_SEQ_CST) 98 99 /* Sanity check that the size of an atomic operation isn't "overly large". 100 * Despite the fact that e.g. i686 has 64-bit atomic operations, we do not 101 * want to use them because we ought not need them, and this lets us do a 102 * bit of sanity checking that other 32-bit hosts might build. 103 * 104 * That said, we have a problem on 64-bit ILP32 hosts in that in order to 105 * sync with TCG_OVERSIZED_GUEST, this must match TCG_TARGET_REG_BITS. 106 * We'd prefer not want to pull in everything else TCG related, so handle 107 * those few cases by hand. 108 * 109 * Note that x32 is fully detected with __x86_64__ + _ILP32, and that for 110 * Sparc we always force the use of sparcv9 in configure. MIPS n32 (ILP32) & 111 * n64 (LP64) ABIs are both detected using __mips64. 112 */ 113 #if defined(__x86_64__) || defined(__sparc__) || defined(__mips64) 114 # define ATOMIC_REG_SIZE 8 115 #else 116 # define ATOMIC_REG_SIZE sizeof(void *) 117 #endif 118 119 /* Weak atomic operations prevent the compiler moving other 120 * loads/stores past the atomic operation load/store. However there is 121 * no explicit memory barrier for the processor. 122 * 123 * The C11 memory model says that variables that are accessed from 124 * different threads should at least be done with __ATOMIC_RELAXED 125 * primitives or the result is undefined. Generally this has little to 126 * no effect on the generated code but not using the atomic primitives 127 * will get flagged by sanitizers as a violation. 128 */ 129 #define qatomic_read__nocheck(ptr) \ 130 __atomic_load_n(ptr, __ATOMIC_RELAXED) 131 132 #define qatomic_read(ptr) \ 133 ({ \ 134 QEMU_BUILD_BUG_ON(sizeof(*ptr) > ATOMIC_REG_SIZE); \ 135 qatomic_read__nocheck(ptr); \ 136 }) 137 138 #define qatomic_set__nocheck(ptr, i) \ 139 __atomic_store_n(ptr, i, __ATOMIC_RELAXED) 140 141 #define qatomic_set(ptr, i) do { \ 142 QEMU_BUILD_BUG_ON(sizeof(*ptr) > ATOMIC_REG_SIZE); \ 143 qatomic_set__nocheck(ptr, i); \ 144 } while(0) 145 146 /* See above: most compilers currently treat consume and acquire the 147 * same, but this slows down qatomic_rcu_read unnecessarily. 148 */ 149 #ifdef __SANITIZE_THREAD__ 150 #define qatomic_rcu_read__nocheck(ptr, valptr) \ 151 __atomic_load(ptr, valptr, __ATOMIC_CONSUME); 152 #else 153 #define qatomic_rcu_read__nocheck(ptr, valptr) \ 154 __atomic_load(ptr, valptr, __ATOMIC_RELAXED); \ 155 smp_read_barrier_depends(); 156 #endif 157 158 #define qatomic_rcu_read(ptr) \ 159 ({ \ 160 QEMU_BUILD_BUG_ON(sizeof(*ptr) > ATOMIC_REG_SIZE); \ 161 typeof_strip_qual(*ptr) _val; \ 162 qatomic_rcu_read__nocheck(ptr, &_val); \ 163 _val; \ 164 }) 165 166 #define qatomic_rcu_set(ptr, i) do { \ 167 QEMU_BUILD_BUG_ON(sizeof(*ptr) > ATOMIC_REG_SIZE); \ 168 __atomic_store_n(ptr, i, __ATOMIC_RELEASE); \ 169 } while(0) 170 171 #define qatomic_load_acquire(ptr) \ 172 ({ \ 173 QEMU_BUILD_BUG_ON(sizeof(*ptr) > ATOMIC_REG_SIZE); \ 174 typeof_strip_qual(*ptr) _val; \ 175 __atomic_load(ptr, &_val, __ATOMIC_ACQUIRE); \ 176 _val; \ 177 }) 178 179 #define qatomic_store_release(ptr, i) do { \ 180 QEMU_BUILD_BUG_ON(sizeof(*ptr) > ATOMIC_REG_SIZE); \ 181 __atomic_store_n(ptr, i, __ATOMIC_RELEASE); \ 182 } while(0) 183 184 185 /* All the remaining operations are fully sequentially consistent */ 186 187 #define qatomic_xchg__nocheck(ptr, i) ({ \ 188 __atomic_exchange_n(ptr, (i), __ATOMIC_SEQ_CST); \ 189 }) 190 191 #define qatomic_xchg(ptr, i) ({ \ 192 QEMU_BUILD_BUG_ON(sizeof(*ptr) > ATOMIC_REG_SIZE); \ 193 qatomic_xchg__nocheck(ptr, i); \ 194 }) 195 196 /* Returns the eventual value, failed or not */ 197 #define qatomic_cmpxchg__nocheck(ptr, old, new) ({ \ 198 typeof_strip_qual(*ptr) _old = (old); \ 199 (void)__atomic_compare_exchange_n(ptr, &_old, new, false, \ 200 __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST); \ 201 _old; \ 202 }) 203 204 #define qatomic_cmpxchg(ptr, old, new) ({ \ 205 QEMU_BUILD_BUG_ON(sizeof(*ptr) > ATOMIC_REG_SIZE); \ 206 qatomic_cmpxchg__nocheck(ptr, old, new); \ 207 }) 208 209 /* Provide shorter names for GCC atomic builtins, return old value */ 210 #define qatomic_fetch_inc(ptr) __atomic_fetch_add(ptr, 1, __ATOMIC_SEQ_CST) 211 #define qatomic_fetch_dec(ptr) __atomic_fetch_sub(ptr, 1, __ATOMIC_SEQ_CST) 212 213 #define qatomic_fetch_add(ptr, n) __atomic_fetch_add(ptr, n, __ATOMIC_SEQ_CST) 214 #define qatomic_fetch_sub(ptr, n) __atomic_fetch_sub(ptr, n, __ATOMIC_SEQ_CST) 215 #define qatomic_fetch_and(ptr, n) __atomic_fetch_and(ptr, n, __ATOMIC_SEQ_CST) 216 #define qatomic_fetch_or(ptr, n) __atomic_fetch_or(ptr, n, __ATOMIC_SEQ_CST) 217 #define qatomic_fetch_xor(ptr, n) __atomic_fetch_xor(ptr, n, __ATOMIC_SEQ_CST) 218 219 #define qatomic_inc_fetch(ptr) __atomic_add_fetch(ptr, 1, __ATOMIC_SEQ_CST) 220 #define qatomic_dec_fetch(ptr) __atomic_sub_fetch(ptr, 1, __ATOMIC_SEQ_CST) 221 #define qatomic_add_fetch(ptr, n) __atomic_add_fetch(ptr, n, __ATOMIC_SEQ_CST) 222 #define qatomic_sub_fetch(ptr, n) __atomic_sub_fetch(ptr, n, __ATOMIC_SEQ_CST) 223 #define qatomic_and_fetch(ptr, n) __atomic_and_fetch(ptr, n, __ATOMIC_SEQ_CST) 224 #define qatomic_or_fetch(ptr, n) __atomic_or_fetch(ptr, n, __ATOMIC_SEQ_CST) 225 #define qatomic_xor_fetch(ptr, n) __atomic_xor_fetch(ptr, n, __ATOMIC_SEQ_CST) 226 227 /* And even shorter names that return void. */ 228 #define qatomic_inc(ptr) \ 229 ((void) __atomic_fetch_add(ptr, 1, __ATOMIC_SEQ_CST)) 230 #define qatomic_dec(ptr) \ 231 ((void) __atomic_fetch_sub(ptr, 1, __ATOMIC_SEQ_CST)) 232 #define qatomic_add(ptr, n) \ 233 ((void) __atomic_fetch_add(ptr, n, __ATOMIC_SEQ_CST)) 234 #define qatomic_sub(ptr, n) \ 235 ((void) __atomic_fetch_sub(ptr, n, __ATOMIC_SEQ_CST)) 236 #define qatomic_and(ptr, n) \ 237 ((void) __atomic_fetch_and(ptr, n, __ATOMIC_SEQ_CST)) 238 #define qatomic_or(ptr, n) \ 239 ((void) __atomic_fetch_or(ptr, n, __ATOMIC_SEQ_CST)) 240 #define qatomic_xor(ptr, n) \ 241 ((void) __atomic_fetch_xor(ptr, n, __ATOMIC_SEQ_CST)) 242 243 #define smp_wmb() smp_mb_release() 244 #define smp_rmb() smp_mb_acquire() 245 246 /* qatomic_mb_read/set semantics map Java volatile variables. They are 247 * less expensive on some platforms (notably POWER) than fully 248 * sequentially consistent operations. 249 * 250 * As long as they are used as paired operations they are safe to 251 * use. See docs/devel/atomics.rst for more discussion. 252 */ 253 254 #define qatomic_mb_read(ptr) \ 255 qatomic_load_acquire(ptr) 256 257 #if !defined(__SANITIZE_THREAD__) && \ 258 (defined(__i386__) || defined(__x86_64__) || defined(__s390x__)) 259 /* This is more efficient than a store plus a fence. */ 260 # define qatomic_mb_set(ptr, i) ((void)qatomic_xchg(ptr, i)) 261 #else 262 # define qatomic_mb_set(ptr, i) \ 263 ({ qatomic_store_release(ptr, i); smp_mb(); }) 264 #endif 265 266 #define qatomic_fetch_inc_nonzero(ptr) ({ \ 267 typeof_strip_qual(*ptr) _oldn = qatomic_read(ptr); \ 268 while (_oldn && qatomic_cmpxchg(ptr, _oldn, _oldn + 1) != _oldn) { \ 269 _oldn = qatomic_read(ptr); \ 270 } \ 271 _oldn; \ 272 }) 273 274 /* 275 * Abstractions to access atomically (i.e. "once") i64/u64 variables. 276 * 277 * The i386 abi is odd in that by default members are only aligned to 278 * 4 bytes, which means that 8-byte types can wind up mis-aligned. 279 * Clang will then warn about this, and emit a call into libatomic. 280 * 281 * Use of these types in structures when they will be used with atomic 282 * operations can avoid this. 283 */ 284 typedef int64_t aligned_int64_t __attribute__((aligned(8))); 285 typedef uint64_t aligned_uint64_t __attribute__((aligned(8))); 286 287 #ifdef CONFIG_ATOMIC64 288 /* Use __nocheck because sizeof(void *) might be < sizeof(u64) */ 289 #define qatomic_read_i64(P) \ 290 _Generic(*(P), int64_t: qatomic_read__nocheck(P)) 291 #define qatomic_read_u64(P) \ 292 _Generic(*(P), uint64_t: qatomic_read__nocheck(P)) 293 #define qatomic_set_i64(P, V) \ 294 _Generic(*(P), int64_t: qatomic_set__nocheck(P, V)) 295 #define qatomic_set_u64(P, V) \ 296 _Generic(*(P), uint64_t: qatomic_set__nocheck(P, V)) 297 298 static inline void qatomic64_init(void) 299 { 300 } 301 #else /* !CONFIG_ATOMIC64 */ 302 int64_t qatomic_read_i64(const int64_t *ptr); 303 uint64_t qatomic_read_u64(const uint64_t *ptr); 304 void qatomic_set_i64(int64_t *ptr, int64_t val); 305 void qatomic_set_u64(uint64_t *ptr, uint64_t val); 306 void qatomic64_init(void); 307 #endif /* !CONFIG_ATOMIC64 */ 308 309 #endif /* QEMU_ATOMIC_H */ 310