include/qemu/atomic.h

   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.txt 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 #ifdef __ATOMIC_RELAXED
  64 /* For C11 atomic ops */
  65
  66 /* Manual memory barriers
  67  *
  68  *__atomic_thread_fence does not include a compiler barrier; instead,
  69  * the barrier is part of __atomic_load/__atomic_store's "volatile-like"
  70  * semantics. If smp_wmb() is a no-op, absence of the barrier means that
  71  * the compiler is free to reorder stores on each side of the barrier.
  72  * Add one here, and similarly in smp_rmb() and smp_read_barrier_depends().
  73  */
  74
  75 #define smp_mb()                     ({ barrier(); __atomic_thread_fence(__ATOMIC_SEQ_CST); })
  76 #define smp_mb_release()             ({ barrier(); __atomic_thread_fence(__ATOMIC_RELEASE); })
  77 #define smp_mb_acquire()             ({ barrier(); __atomic_thread_fence(__ATOMIC_ACQUIRE); })
  78
  79 /* Most compilers currently treat consume and acquire the same, but really
  80  * no processors except Alpha need a barrier here.  Leave it in if
  81  * using Thread Sanitizer to avoid warnings, otherwise optimize it away.
  82  */
  83 #if defined(__SANITIZE_THREAD__)
  84 #define smp_read_barrier_depends()   ({ barrier(); __atomic_thread_fence(__ATOMIC_CONSUME); })
  85 #elif defined(__alpha__)
  86 #define smp_read_barrier_depends()   asm volatile("mb":::"memory")
  87 #else
  88 #define smp_read_barrier_depends()   barrier()
  89 #endif
  90
  91 /* Sanity check that the size of an atomic operation isn't "overly large".
  92  * Despite the fact that e.g. i686 has 64-bit atomic operations, we do not
  93  * want to use them because we ought not need them, and this lets us do a
  94  * bit of sanity checking that other 32-bit hosts might build.
  95  *
  96  * That said, we have a problem on 64-bit ILP32 hosts in that in order to
  97  * sync with TCG_OVERSIZED_GUEST, this must match TCG_TARGET_REG_BITS.
  98  * We'd prefer not want to pull in everything else TCG related, so handle
  99  * those few cases by hand.
 100  *
 101  * Note that x32 is fully detected with __x64_64__ + _ILP32, and that for
 102  * Sparc we always force the use of sparcv9 in configure.
 103  */
 104 #if defined(__x86_64__) || defined(__sparc__)
 105 # define ATOMIC_REG_SIZE  8
 106 #else
 107 # define ATOMIC_REG_SIZE  sizeof(void *)
 108 #endif
 109
 110 /* Weak atomic operations prevent the compiler moving other
 111  * loads/stores past the atomic operation load/store. However there is
 112  * no explicit memory barrier for the processor.
 113  *
 114  * The C11 memory model says that variables that are accessed from
 115  * different threads should at least be done with __ATOMIC_RELAXED
 116  * primitives or the result is undefined. Generally this has little to
 117  * no effect on the generated code but not using the atomic primitives
 118  * will get flagged by sanitizers as a violation.
 119  */
 120 #define atomic_read__nocheck(ptr) \
 121     __atomic_load_n(ptr, __ATOMIC_RELAXED)
 122
 123 #define atomic_read(ptr)                              \
 124     ({                                                \
 125     QEMU_BUILD_BUG_ON(sizeof(*ptr) > ATOMIC_REG_SIZE); \
 126     atomic_read__nocheck(ptr);                        \
 127     })
 128
 129 #define atomic_set__nocheck(ptr, i) \
 130     __atomic_store_n(ptr, i, __ATOMIC_RELAXED)
 131
 132 #define atomic_set(ptr, i)  do {                      \
 133     QEMU_BUILD_BUG_ON(sizeof(*ptr) > ATOMIC_REG_SIZE); \
 134     atomic_set__nocheck(ptr, i);                      \
 135 } while(0)
 136
 137 /* See above: most compilers currently treat consume and acquire the
 138  * same, but this slows down atomic_rcu_read unnecessarily.
 139  */
 140 #ifdef __SANITIZE_THREAD__
 141 #define atomic_rcu_read__nocheck(ptr, valptr)           \
 142     __atomic_load(ptr, valptr, __ATOMIC_CONSUME);
 143 #else
 144 #define atomic_rcu_read__nocheck(ptr, valptr)           \
 145     __atomic_load(ptr, valptr, __ATOMIC_RELAXED);       \
 146     smp_read_barrier_depends();
 147 #endif
 148
 149 #define atomic_rcu_read(ptr)                          \
 150     ({                                                \
 151     QEMU_BUILD_BUG_ON(sizeof(*ptr) > ATOMIC_REG_SIZE); \
 152     typeof_strip_qual(*ptr) _val;                     \
 153     atomic_rcu_read__nocheck(ptr, &_val);             \
 154     _val;                                             \
 155     })
 156
 157 #define atomic_rcu_set(ptr, i) do {                   \
 158     QEMU_BUILD_BUG_ON(sizeof(*ptr) > ATOMIC_REG_SIZE); \
 159     __atomic_store_n(ptr, i, __ATOMIC_RELEASE);       \
 160 } while(0)
 161
 162 #define atomic_load_acquire(ptr)                        \
 163     ({                                                  \
 164     QEMU_BUILD_BUG_ON(sizeof(*ptr) > ATOMIC_REG_SIZE);  \
 165     typeof_strip_qual(*ptr) _val;                       \
 166     __atomic_load(ptr, &_val, __ATOMIC_ACQUIRE);        \
 167     _val;                                               \
 168     })
 169
 170 #define atomic_store_release(ptr, i)  do {              \
 171     QEMU_BUILD_BUG_ON(sizeof(*ptr) > ATOMIC_REG_SIZE);  \
 172     __atomic_store_n(ptr, i, __ATOMIC_RELEASE);         \
 173 } while(0)
 174
 175
 176 /* All the remaining operations are fully sequentially consistent */
 177
 178 #define atomic_xchg__nocheck(ptr, i)    ({                  \
 179     __atomic_exchange_n(ptr, (i), __ATOMIC_SEQ_CST);        \
 180 })
 181
 182 #define atomic_xchg(ptr, i)    ({                           \
 183     QEMU_BUILD_BUG_ON(sizeof(*ptr) > ATOMIC_REG_SIZE);      \
 184     atomic_xchg__nocheck(ptr, i);                           \
 185 })
 186
 187 /* Returns the eventual value, failed or not */
 188 #define atomic_cmpxchg__nocheck(ptr, old, new)    ({                    \
 189     typeof_strip_qual(*ptr) _old = (old);                               \
 190     __atomic_compare_exchange_n(ptr, &_old, new, false,                 \
 191                               __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST);      \
 192     _old;                                                               \
 193 })
 194
 195 #define atomic_cmpxchg(ptr, old, new)    ({                             \
 196     QEMU_BUILD_BUG_ON(sizeof(*ptr) > ATOMIC_REG_SIZE);                  \
 197     atomic_cmpxchg__nocheck(ptr, old, new);                             \
 198 })
 199
 200 /* Provide shorter names for GCC atomic builtins, return old value */
 201 #define atomic_fetch_inc(ptr)  __atomic_fetch_add(ptr, 1, __ATOMIC_SEQ_CST)
 202 #define atomic_fetch_dec(ptr)  __atomic_fetch_sub(ptr, 1, __ATOMIC_SEQ_CST)
 203 #define atomic_fetch_add(ptr, n) __atomic_fetch_add(ptr, n, __ATOMIC_SEQ_CST)
 204 #define atomic_fetch_sub(ptr, n) __atomic_fetch_sub(ptr, n, __ATOMIC_SEQ_CST)
 205 #define atomic_fetch_and(ptr, n) __atomic_fetch_and(ptr, n, __ATOMIC_SEQ_CST)
 206 #define atomic_fetch_or(ptr, n)  __atomic_fetch_or(ptr, n, __ATOMIC_SEQ_CST)
 207 #define atomic_fetch_xor(ptr, n) __atomic_fetch_xor(ptr, n, __ATOMIC_SEQ_CST)
 208
 209 #define atomic_inc_fetch(ptr)    __atomic_add_fetch(ptr, 1, __ATOMIC_SEQ_CST)
 210 #define atomic_dec_fetch(ptr)    __atomic_sub_fetch(ptr, 1, __ATOMIC_SEQ_CST)
 211 #define atomic_add_fetch(ptr, n) __atomic_add_fetch(ptr, n, __ATOMIC_SEQ_CST)
 212 #define atomic_sub_fetch(ptr, n) __atomic_sub_fetch(ptr, n, __ATOMIC_SEQ_CST)
 213 #define atomic_and_fetch(ptr, n) __atomic_and_fetch(ptr, n, __ATOMIC_SEQ_CST)
 214 #define atomic_or_fetch(ptr, n)  __atomic_or_fetch(ptr, n, __ATOMIC_SEQ_CST)
 215 #define atomic_xor_fetch(ptr, n) __atomic_xor_fetch(ptr, n, __ATOMIC_SEQ_CST)
 216
 217 /* And even shorter names that return void.  */
 218 #define atomic_inc(ptr)    ((void) __atomic_fetch_add(ptr, 1, __ATOMIC_SEQ_CST))
 219 #define atomic_dec(ptr)    ((void) __atomic_fetch_sub(ptr, 1, __ATOMIC_SEQ_CST))
 220 #define atomic_add(ptr, n) ((void) __atomic_fetch_add(ptr, n, __ATOMIC_SEQ_CST))
 221 #define atomic_sub(ptr, n) ((void) __atomic_fetch_sub(ptr, n, __ATOMIC_SEQ_CST))
 222 #define atomic_and(ptr, n) ((void) __atomic_fetch_and(ptr, n, __ATOMIC_SEQ_CST))
 223 #define atomic_or(ptr, n)  ((void) __atomic_fetch_or(ptr, n, __ATOMIC_SEQ_CST))
 224 #define atomic_xor(ptr, n) ((void) __atomic_fetch_xor(ptr, n, __ATOMIC_SEQ_CST))
 225
 226 #else /* __ATOMIC_RELAXED */
 227
 228 /*
 229  * We use GCC builtin if it's available, as that can use mfence on
 230  * 32-bit as well, e.g. if built with -march=pentium-m. However, on
 231  * i386 the spec is buggy, and the implementation followed it until
 232  * 4.3 (http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36793).
 233  */
 234 #if defined(__i386__) || defined(__x86_64__)
 235 #if !QEMU_GNUC_PREREQ(4, 4)
 236 #if defined __x86_64__
 237 #define smp_mb()    ({ asm volatile("mfence" ::: "memory"); (void)0; })
 238 #else
 239 #define smp_mb()    ({ asm volatile("lock; addl $0,0(%%esp) " ::: "memory"); (void)0; })
 240 #endif
 241 #endif
 242 #endif
 243
 244
 245 #ifdef __alpha__
 246 #define smp_read_barrier_depends()   asm volatile("mb":::"memory")
 247 #endif
 248
 249 #if defined(__i386__) || defined(__x86_64__) || defined(__s390x__)
 250
 251 /*
 252  * Because of the strongly ordered storage model, wmb() and rmb() are nops
 253  * here (a compiler barrier only).  QEMU doesn't do accesses to write-combining
 254  * qemu memory or non-temporal load/stores from C code.
 255  */
 256 #define smp_mb_release()   barrier()
 257 #define smp_mb_acquire()   barrier()
 258
 259 /*
 260  * __sync_lock_test_and_set() is documented to be an acquire barrier only,
 261  * but it is a full barrier at the hardware level.  Add a compiler barrier
 262  * to make it a full barrier also at the compiler level.
 263  */
 264 #define atomic_xchg(ptr, i)    (barrier(), __sync_lock_test_and_set(ptr, i))
 265
 266 #elif defined(_ARCH_PPC)
 267
 268 /*
 269  * We use an eieio() for wmb() on powerpc.  This assumes we don't
 270  * need to order cacheable and non-cacheable stores with respect to
 271  * each other.
 272  *
 273  * smp_mb has the same problem as on x86 for not-very-new GCC
 274  * (http://patchwork.ozlabs.org/patch/126184/, Nov 2011).
 275  */
 276 #define smp_wmb()          ({ asm volatile("eieio" ::: "memory"); (void)0; })
 277 #if defined(__powerpc64__)
 278 #define smp_mb_release()   ({ asm volatile("lwsync" ::: "memory"); (void)0; })
 279 #define smp_mb_acquire()   ({ asm volatile("lwsync" ::: "memory"); (void)0; })
 280 #else
 281 #define smp_mb_release()   ({ asm volatile("sync" ::: "memory"); (void)0; })
 282 #define smp_mb_acquire()   ({ asm volatile("sync" ::: "memory"); (void)0; })
 283 #endif
 284 #define smp_mb()           ({ asm volatile("sync" ::: "memory"); (void)0; })
 285
 286 #endif /* _ARCH_PPC */
 287
 288 /*
 289  * For (host) platforms we don't have explicit barrier definitions
 290  * for, we use the gcc __sync_synchronize() primitive to generate a
 291  * full barrier.  This should be safe on all platforms, though it may
 292  * be overkill for smp_mb_acquire() and smp_mb_release().
 293  */
 294 #ifndef smp_mb
 295 #define smp_mb()           __sync_synchronize()
 296 #endif
 297
 298 #ifndef smp_mb_acquire
 299 #define smp_mb_acquire()   __sync_synchronize()
 300 #endif
 301
 302 #ifndef smp_mb_release
 303 #define smp_mb_release()   __sync_synchronize()
 304 #endif
 305
 306 #ifndef smp_read_barrier_depends
 307 #define smp_read_barrier_depends()   barrier()
 308 #endif
 309
 310 /* These will only be atomic if the processor does the fetch or store
 311  * in a single issue memory operation
 312  */
 313 #define atomic_read__nocheck(p)   (*(__typeof__(*(p)) volatile*) (p))
 314 #define atomic_set__nocheck(p, i) ((*(__typeof__(*(p)) volatile*) (p)) = (i))
 315
 316 #define atomic_read(ptr)       atomic_read__nocheck(ptr)
 317 #define atomic_set(ptr, i)     atomic_set__nocheck(ptr,i)
 318
 319 /**
 320  * atomic_rcu_read - reads a RCU-protected pointer to a local variable
 321  * into a RCU read-side critical section. The pointer can later be safely
 322  * dereferenced within the critical section.
 323  *
 324  * This ensures that the pointer copy is invariant thorough the whole critical
 325  * section.
 326  *
 327  * Inserts memory barriers on architectures that require them (currently only
 328  * Alpha) and documents which pointers are protected by RCU.
 329  *
 330  * atomic_rcu_read also includes a compiler barrier to ensure that
 331  * value-speculative optimizations (e.g. VSS: Value Speculation
 332  * Scheduling) does not perform the data read before the pointer read
 333  * by speculating the value of the pointer.
 334  *
 335  * Should match atomic_rcu_set(), atomic_xchg(), atomic_cmpxchg().
 336  */
 337 #define atomic_rcu_read(ptr)    ({                \
 338     typeof(*ptr) _val = atomic_read(ptr);         \
 339     smp_read_barrier_depends();                   \
 340     _val;                                         \
 341 })
 342
 343 /**
 344  * atomic_rcu_set - assigns (publicizes) a pointer to a new data structure
 345  * meant to be read by RCU read-side critical sections.
 346  *
 347  * Documents which pointers will be dereferenced by RCU read-side critical
 348  * sections and adds the required memory barriers on architectures requiring
 349  * them. It also makes sure the compiler does not reorder code initializing the
 350  * data structure before its publication.
 351  *
 352  * Should match atomic_rcu_read().
 353  */
 354 #define atomic_rcu_set(ptr, i)  do {              \
 355     smp_wmb();                                    \
 356     atomic_set(ptr, i);                           \
 357 } while (0)
 358
 359 #define atomic_load_acquire(ptr)    ({      \
 360     typeof(*ptr) _val = atomic_read(ptr);   \
 361     smp_mb_acquire();                       \
 362     _val;                                   \
 363 })
 364
 365 #define atomic_store_release(ptr, i)  do {  \
 366     smp_mb_release();                       \
 367     atomic_set(ptr, i);                     \
 368 } while (0)
 369
 370 #ifndef atomic_xchg
 371 #if defined(__clang__)
 372 #define atomic_xchg(ptr, i)    __sync_swap(ptr, i)
 373 #else
 374 /* __sync_lock_test_and_set() is documented to be an acquire barrier only.  */
 375 #define atomic_xchg(ptr, i)    (smp_mb(), __sync_lock_test_and_set(ptr, i))
 376 #endif
 377 #endif
 378 #define atomic_xchg__nocheck  atomic_xchg
 379
 380 /* Provide shorter names for GCC atomic builtins.  */
 381 #define atomic_fetch_inc(ptr)  __sync_fetch_and_add(ptr, 1)
 382 #define atomic_fetch_dec(ptr)  __sync_fetch_and_add(ptr, -1)
 383 #define atomic_fetch_add(ptr, n) __sync_fetch_and_add(ptr, n)
 384 #define atomic_fetch_sub(ptr, n) __sync_fetch_and_sub(ptr, n)
 385 #define atomic_fetch_and(ptr, n) __sync_fetch_and_and(ptr, n)
 386 #define atomic_fetch_or(ptr, n) __sync_fetch_and_or(ptr, n)
 387 #define atomic_fetch_xor(ptr, n) __sync_fetch_and_xor(ptr, n)
 388
 389 #define atomic_inc_fetch(ptr)  __sync_add_and_fetch(ptr, 1)
 390 #define atomic_dec_fetch(ptr)  __sync_add_and_fetch(ptr, -1)
 391 #define atomic_add_fetch(ptr, n) __sync_add_and_fetch(ptr, n)
 392 #define atomic_sub_fetch(ptr, n) __sync_sub_and_fetch(ptr, n)
 393 #define atomic_and_fetch(ptr, n) __sync_and_and_fetch(ptr, n)
 394 #define atomic_or_fetch(ptr, n) __sync_or_and_fetch(ptr, n)
 395 #define atomic_xor_fetch(ptr, n) __sync_xor_and_fetch(ptr, n)
 396
 397 #define atomic_cmpxchg(ptr, old, new) __sync_val_compare_and_swap(ptr, old, new)
 398 #define atomic_cmpxchg__nocheck(ptr, old, new)  atomic_cmpxchg(ptr, old, new)
 399
 400 /* And even shorter names that return void.  */
 401 #define atomic_inc(ptr)        ((void) __sync_fetch_and_add(ptr, 1))
 402 #define atomic_dec(ptr)        ((void) __sync_fetch_and_add(ptr, -1))
 403 #define atomic_add(ptr, n)     ((void) __sync_fetch_and_add(ptr, n))
 404 #define atomic_sub(ptr, n)     ((void) __sync_fetch_and_sub(ptr, n))
 405 #define atomic_and(ptr, n)     ((void) __sync_fetch_and_and(ptr, n))
 406 #define atomic_or(ptr, n)      ((void) __sync_fetch_and_or(ptr, n))
 407 #define atomic_xor(ptr, n)     ((void) __sync_fetch_and_xor(ptr, n))
 408
 409 #endif /* __ATOMIC_RELAXED */
 410
 411 #ifndef smp_wmb
 412 #define smp_wmb()   smp_mb_release()
 413 #endif
 414 #ifndef smp_rmb
 415 #define smp_rmb()   smp_mb_acquire()
 416 #endif
 417
 418 /* This is more efficient than a store plus a fence.  */
 419 #if !defined(__SANITIZE_THREAD__)
 420 #if defined(__i386__) || defined(__x86_64__) || defined(__s390x__)
 421 #define atomic_mb_set(ptr, i)  ((void)atomic_xchg(ptr, i))
 422 #endif
 423 #endif
 424
 425 /* atomic_mb_read/set semantics map Java volatile variables. They are
 426  * less expensive on some platforms (notably POWER) than fully
 427  * sequentially consistent operations.
 428  *
 429  * As long as they are used as paired operations they are safe to
 430  * use. See docs/devel/atomics.txt for more discussion.
 431  */
 432
 433 #ifndef atomic_mb_read
 434 #define atomic_mb_read(ptr)                             \
 435     atomic_load_acquire(ptr)
 436 #endif
 437
 438 #ifndef atomic_mb_set
 439 #define atomic_mb_set(ptr, i)  do {                     \
 440     atomic_store_release(ptr, i);                       \
 441     smp_mb();                                           \
 442 } while(0)
 443 #endif
 444
 445 #endif /* QEMU_ATOMIC_H */