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qemu-e2k/include/qemu/atomic.h
Paolo Bonzini 06831001ac atomics: eliminate mb_read/mb_set 
qatomic_mb_read and qatomic_mb_set were the very first atomic primitives
introduced for QEMU; their semantics are unclear and they provide a false
sense of safety.

The last use of qatomic_mb_read() has been removed, so delete it.
qatomic_mb_set() instead can survive as an optimized
qatomic_set()+smp_mb(), similar to Linux's smp_store_mb(), but
rename it to qatomic_set_mb() to match the order of the two
operations.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2023-06-06 09:42:14 +02:00

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/*
* Simple interface for atomic operations.
*
* Copyright (C) 2013 Red Hat, Inc.
*
* Author: Paolo Bonzini <pbonzini@redhat.com>
*
* 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/devel/atomics.rst for discussion about the guarantees each
* atomic primitive is meant to provide.
*/
#ifndef QEMU_ATOMIC_H
#define QEMU_ATOMIC_H
#include "compiler.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))))))
#ifndef __ATOMIC_RELAXED
#error "Expecting C11 atomic ops"
#endif
/* 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.
*/
#ifdef QEMU_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
/*
* A signal barrier forces all pending local memory ops to be observed before
* a SIGSEGV is delivered to the *same* thread. In practice this is exactly
* the same as barrier(), but since we have the correct builtin, use it.
*/
#define signal_barrier() __atomic_signal_fence(__ATOMIC_SEQ_CST)
/* 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 __x86_64__ + _ILP32, and that for
* Sparc we always force the use of sparcv9 in configure. MIPS n32 (ILP32) &
* n64 (LP64) ABIs are both detected using __mips64.
*/
#if defined(__x86_64__) || defined(__sparc__) || defined(__mips64)
# 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 qatomic_read__nocheck(ptr) \
__atomic_load_n(ptr, __ATOMIC_RELAXED)
#define qatomic_read(ptr) \
({ \
qemu_build_assert(sizeof(*ptr) <= ATOMIC_REG_SIZE); \
qatomic_read__nocheck(ptr); \
})
#define qatomic_set__nocheck(ptr, i) \
__atomic_store_n(ptr, i, __ATOMIC_RELAXED)
#define qatomic_set(ptr, i) do { \
qemu_build_assert(sizeof(*ptr) <= ATOMIC_REG_SIZE); \
qatomic_set__nocheck(ptr, i); \
} while(0)
/* See above: most compilers currently treat consume and acquire the
* same, but this slows down qatomic_rcu_read unnecessarily.
*/
#ifdef QEMU_SANITIZE_THREAD
#define qatomic_rcu_read__nocheck(ptr, valptr) \
__atomic_load(ptr, valptr, __ATOMIC_CONSUME);
#else
#define qatomic_rcu_read__nocheck(ptr, valptr) \
__atomic_load(ptr, valptr, __ATOMIC_RELAXED); \
smp_read_barrier_depends();
#endif
#define qatomic_rcu_read(ptr) \
({ \
qemu_build_assert(sizeof(*ptr) <= ATOMIC_REG_SIZE); \
typeof_strip_qual(*ptr) _val; \
qatomic_rcu_read__nocheck(ptr, &_val); \
_val; \
})
#define qatomic_rcu_set(ptr, i) do { \
qemu_build_assert(sizeof(*ptr) <= ATOMIC_REG_SIZE); \
__atomic_store_n(ptr, i, __ATOMIC_RELEASE); \
} while(0)
#define qatomic_load_acquire(ptr) \
({ \
qemu_build_assert(sizeof(*ptr) <= ATOMIC_REG_SIZE); \
typeof_strip_qual(*ptr) _val; \
__atomic_load(ptr, &_val, __ATOMIC_ACQUIRE); \
_val; \
})
#define qatomic_store_release(ptr, i) do { \
qemu_build_assert(sizeof(*ptr) <= ATOMIC_REG_SIZE); \
__atomic_store_n(ptr, i, __ATOMIC_RELEASE); \
} while(0)
/* All the remaining operations are fully sequentially consistent */
#define qatomic_xchg__nocheck(ptr, i) ({ \
__atomic_exchange_n(ptr, (i), __ATOMIC_SEQ_CST); \
})
#define qatomic_xchg(ptr, i) ({ \
qemu_build_assert(sizeof(*ptr) <= ATOMIC_REG_SIZE); \
qatomic_xchg__nocheck(ptr, i); \
})
/* Returns the eventual value, failed or not */
#define qatomic_cmpxchg__nocheck(ptr, old, new) ({ \
typeof_strip_qual(*ptr) _old = (old); \
(void)__atomic_compare_exchange_n(ptr, &_old, new, false, \
__ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST); \
_old; \
})
#define qatomic_cmpxchg(ptr, old, new) ({ \
qemu_build_assert(sizeof(*ptr) <= ATOMIC_REG_SIZE); \
qatomic_cmpxchg__nocheck(ptr, old, new); \
})
/* Provide shorter names for GCC atomic builtins, return old value */
#define qatomic_fetch_inc(ptr) __atomic_fetch_add(ptr, 1, __ATOMIC_SEQ_CST)
#define qatomic_fetch_dec(ptr) __atomic_fetch_sub(ptr, 1, __ATOMIC_SEQ_CST)
#define qatomic_fetch_add(ptr, n) __atomic_fetch_add(ptr, n, __ATOMIC_SEQ_CST)
#define qatomic_fetch_sub(ptr, n) __atomic_fetch_sub(ptr, n, __ATOMIC_SEQ_CST)
#define qatomic_fetch_and(ptr, n) __atomic_fetch_and(ptr, n, __ATOMIC_SEQ_CST)
#define qatomic_fetch_or(ptr, n) __atomic_fetch_or(ptr, n, __ATOMIC_SEQ_CST)
#define qatomic_fetch_xor(ptr, n) __atomic_fetch_xor(ptr, n, __ATOMIC_SEQ_CST)
#define qatomic_inc_fetch(ptr) __atomic_add_fetch(ptr, 1, __ATOMIC_SEQ_CST)
#define qatomic_dec_fetch(ptr) __atomic_sub_fetch(ptr, 1, __ATOMIC_SEQ_CST)
#define qatomic_add_fetch(ptr, n) __atomic_add_fetch(ptr, n, __ATOMIC_SEQ_CST)
#define qatomic_sub_fetch(ptr, n) __atomic_sub_fetch(ptr, n, __ATOMIC_SEQ_CST)
#define qatomic_and_fetch(ptr, n) __atomic_and_fetch(ptr, n, __ATOMIC_SEQ_CST)
#define qatomic_or_fetch(ptr, n) __atomic_or_fetch(ptr, n, __ATOMIC_SEQ_CST)
#define qatomic_xor_fetch(ptr, n) __atomic_xor_fetch(ptr, n, __ATOMIC_SEQ_CST)
/* And even shorter names that return void. */
#define qatomic_inc(ptr) \
((void) __atomic_fetch_add(ptr, 1, __ATOMIC_SEQ_CST))
#define qatomic_dec(ptr) \
((void) __atomic_fetch_sub(ptr, 1, __ATOMIC_SEQ_CST))
#define qatomic_add(ptr, n) \
((void) __atomic_fetch_add(ptr, n, __ATOMIC_SEQ_CST))
#define qatomic_sub(ptr, n) \
((void) __atomic_fetch_sub(ptr, n, __ATOMIC_SEQ_CST))
#define qatomic_and(ptr, n) \
((void) __atomic_fetch_and(ptr, n, __ATOMIC_SEQ_CST))
#define qatomic_or(ptr, n) \
((void) __atomic_fetch_or(ptr, n, __ATOMIC_SEQ_CST))
#define qatomic_xor(ptr, n) \
((void) __atomic_fetch_xor(ptr, n, __ATOMIC_SEQ_CST))
#define smp_wmb() smp_mb_release()
#define smp_rmb() smp_mb_acquire()
/*
* SEQ_CST is weaker than the older __sync_* builtins and Linux
* kernel read-modify-write atomics. Provide a macro to obtain
* the same semantics.
*/
#if !defined(QEMU_SANITIZE_THREAD) && \
(defined(__i386__) || defined(__x86_64__) || defined(__s390x__))
# define smp_mb__before_rmw() signal_barrier()
# define smp_mb__after_rmw() signal_barrier()
#else
# define smp_mb__before_rmw() smp_mb()
# define smp_mb__after_rmw() smp_mb()
#endif
/*
* On some architectures, qatomic_set_mb is more efficient than a store
* plus a fence.
*/
#if !defined(QEMU_SANITIZE_THREAD) && \
(defined(__i386__) || defined(__x86_64__) || defined(__s390x__))
# define qatomic_set_mb(ptr, i) \
({ (void)qatomic_xchg(ptr, i); smp_mb__after_rmw(); })
#else
# define qatomic_set_mb(ptr, i) \
({ qatomic_store_release(ptr, i); smp_mb(); })
#endif
#define qatomic_fetch_inc_nonzero(ptr) ({ \
typeof_strip_qual(*ptr) _oldn = qatomic_read(ptr); \
while (_oldn && qatomic_cmpxchg(ptr, _oldn, _oldn + 1) != _oldn) { \
_oldn = qatomic_read(ptr); \
} \
_oldn; \
})
/*
* Abstractions to access atomically (i.e. "once") i64/u64 variables.
*
* The i386 abi is odd in that by default members are only aligned to
* 4 bytes, which means that 8-byte types can wind up mis-aligned.
* Clang will then warn about this, and emit a call into libatomic.
*
* Use of these types in structures when they will be used with atomic
* operations can avoid this.
*/
typedef int64_t aligned_int64_t __attribute__((aligned(8)));
typedef uint64_t aligned_uint64_t __attribute__((aligned(8)));
#ifdef CONFIG_ATOMIC64
/* Use __nocheck because sizeof(void *) might be < sizeof(u64) */
#define qatomic_read_i64(P) \
_Generic(*(P), int64_t: qatomic_read__nocheck(P))
#define qatomic_read_u64(P) \
_Generic(*(P), uint64_t: qatomic_read__nocheck(P))
#define qatomic_set_i64(P, V) \
_Generic(*(P), int64_t: qatomic_set__nocheck(P, V))
#define qatomic_set_u64(P, V) \
_Generic(*(P), uint64_t: qatomic_set__nocheck(P, V))
static inline void qatomic64_init(void)
{
}
#else /* !CONFIG_ATOMIC64 */
int64_t qatomic_read_i64(const int64_t *ptr);
uint64_t qatomic_read_u64(const uint64_t *ptr);
void qatomic_set_i64(int64_t *ptr, int64_t val);
void qatomic_set_u64(uint64_t *ptr, uint64_t val);
void qatomic64_init(void);
#endif /* !CONFIG_ATOMIC64 */
#endif /* QEMU_ATOMIC_H */
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