mirrors/qemu
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

include/qemu/atomic.h: default to __atomic functions

Browse Source 
The __atomic primitives have been available since GCC 4.7 and provide
a richer interface for describing memory ordering requirements. As a
bonus by using the primitives instead of hand-rolled functions we can
use tools such as the ThreadSanitizer which need the use of well
defined APIs for its analysis.

If we have __ATOMIC defines we exclusively use the __atomic primitives
for all our atomic access. Otherwise we fall back to the mixture of
__sync and hand-rolled barrier cases.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <1453976119-24372-4-git-send-email-alex.bennee@linaro.org>
[Use __ATOMIC_SEQ_CST for atomic_mb_read/atomic_mb_set on !POWER. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Alex Bennée 2016-01-28 10:15:17 +00:00 committed by Paolo Bonzini
parent 977a82ab56
commit a0aa44b488
1 changed files with 131 additions and 61 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

192
include/qemu/atomic.h
View File

@ -8,6 +8,8 @@
* 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
@ -15,12 +17,130 @@
#include "qemu/compiler.h"
/* For C11 atomic ops */
/* Compiler barrier */
#define barrier() ({ asm volatile("" ::: "memory"); (void)0; })
#ifndef __ATOMIC_RELAXED
#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); barrier(); })
#define smp_wmb() ({ barrier(); __atomic_thread_fence(__ATOMIC_RELEASE); barrier(); })
#define smp_rmb() ({ barrier(); __atomic_thread_fence(__ATOMIC_ACQUIRE); barrier(); })
#define smp_read_barrier_depends() ({ barrier(); __atomic_thread_fence(__ATOMIC_CONSUME); barrier(); })
/* 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.
*/
#define atomic_read(ptr) \
({ \
typeof(*ptr) _val; \
__atomic_load(ptr, &_val, __ATOMIC_RELAXED); \
_val; \
})
#define atomic_set(ptr, i) do { \
typeof(*ptr) _val = (i); \
__atomic_store(ptr, &_val, __ATOMIC_RELAXED); \
} while(0)
/* Atomic RCU operations imply weak memory barriers */
#define atomic_rcu_read(ptr) \
({ \
typeof(*ptr) _val; \
__atomic_load(ptr, &_val, __ATOMIC_CONSUME); \
_val; \
})
#define atomic_rcu_set(ptr, i) do { \
typeof(*ptr) _val = (i); \
__atomic_store(ptr, &_val, __ATOMIC_RELEASE); \
} while(0)
/* atomic_mb_read/set semantics map Java volatile variables. They are
* less expensive on some platforms (notably POWER & ARMv7) 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.
*/
#if defined(_ARCH_PPC)
#define atomic_mb_read(ptr) \
({ \
typeof(*ptr) _val; \
__atomic_load(ptr, &_val, __ATOMIC_RELAXED); \
smp_rmb(); \
_val; \
})
#define atomic_mb_set(ptr, i) do { \
typeof(*ptr) _val = (i); \
smp_wmb(); \
__atomic_store(ptr, &_val, __ATOMIC_RELAXED); \
smp_mb(); \
} while(0)
#else
#define atomic_mb_read(ptr) \
({ \
typeof(*ptr) _val; \
__atomic_load(ptr, &_val, __ATOMIC_SEQ_CST); \
_val; \
})
#define atomic_mb_set(ptr, i) do { \
typeof(*ptr) _val = (i); \
__atomic_store(ptr, &_val, __ATOMIC_SEQ_CST); \
} while(0)
#endif
/* All the remaining operations are fully sequentially consistent */
#define atomic_xchg(ptr, i) ({ \
typeof(*ptr) _new = (i), _old; \
__atomic_exchange(ptr, &_new, &_old, __ATOMIC_SEQ_CST); \
_old; \
})
/* Returns the eventual value, failed or not */
#define atomic_cmpxchg(ptr, old, new) \
({ \
typeof(*ptr) _old = (old), _new = (new); \
__atomic_compare_exchange(ptr, &_old, &_new, false, \
__ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST); \
_old; \
})
/* 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)
/* 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))
#else /* __ATOMIC_RELAXED */
/*
* We use GCC builtin if it's available, as that can use mfence on
@ -85,8 +205,6 @@
#endif /* _ARCH_PPC */
#endif /* C11 atomics */
/*
* For (host) platforms we don't have explicit barrier definitions
* for, we use the gcc __sync_synchronize() primitive to generate a
@ -98,42 +216,22 @@
#endif
#ifndef smp_wmb
#ifdef __ATOMIC_RELEASE
/* __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_wmb() ({ barrier(); __atomic_thread_fence(__ATOMIC_RELEASE); barrier(); })
#else
#define smp_wmb() __sync_synchronize()
#endif
#endif
#ifndef smp_rmb
#ifdef __ATOMIC_ACQUIRE
#define smp_rmb() ({ barrier(); __atomic_thread_fence(__ATOMIC_ACQUIRE); barrier(); })
#else
#define smp_rmb() __sync_synchronize()
#endif
#endif
#ifndef smp_read_barrier_depends
#ifdef __ATOMIC_CONSUME
#define smp_read_barrier_depends() ({ barrier(); __atomic_thread_fence(__ATOMIC_CONSUME); barrier(); })
#else
#define smp_read_barrier_depends() barrier()
#endif
#endif
#ifndef atomic_read
/* These will only be atomic if the processor does the fetch or store
* in a single issue memory operation
*/
#define atomic_read(ptr) (*(__typeof__(*ptr) volatile*) (ptr))
#endif
#ifndef atomic_set
#define atomic_set(ptr, i) ((*(__typeof__(*ptr) volatile*) (ptr)) = (i))
#endif
/**
* atomic_rcu_read - reads a RCU-protected pointer to a local variable
@ -146,30 +244,18 @@
* Inserts memory barriers on architectures that require them (currently only
* Alpha) and documents which pointers are protected by RCU.
*
* Unless the __ATOMIC_CONSUME memory order is available, 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. On new
* enough compilers, atomic_load takes care of such concern about
* dependency-breaking optimizations.
* 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().
*/
#ifndef atomic_rcu_read
#ifdef __ATOMIC_CONSUME
#define atomic_rcu_read(ptr) ({ \
typeof(*ptr) _val; \
__atomic_load(ptr, &_val, __ATOMIC_CONSUME); \
_val; \
})
#else
#define atomic_rcu_read(ptr) ({ \
typeof(*ptr) _val = atomic_read(ptr); \
smp_read_barrier_depends(); \
_val; \
})
#endif
#endif
/**
* atomic_rcu_set - assigns (publicizes) a pointer to a new data structure
@ -182,19 +268,10 @@
*
* Should match atomic_rcu_read().
*/
#ifndef atomic_rcu_set
#ifdef __ATOMIC_RELEASE
#define atomic_rcu_set(ptr, i) do { \
typeof(*ptr) _val = (i); \
__atomic_store(ptr, &_val, __ATOMIC_RELEASE); \
} while(0)
#else
#define atomic_rcu_set(ptr, i) do { \
smp_wmb(); \
atomic_set(ptr, i); \
} while (0)
#endif
#endif
/* These have the same semantics as Java volatile variables.
* See http://gee.cs.oswego.edu/dl/jmm/cookbook.html:
@ -218,13 +295,11 @@
* (see docs/atomics.txt), and I'm not sure that __ATOMIC_ACQ_REL is enough.
* Just always use the barriers manually by the rules above.
*/
#ifndef atomic_mb_read
#define atomic_mb_read(ptr) ({ \
typeof(*ptr) _val = atomic_read(ptr); \
smp_rmb(); \
_val; \
})
#endif
#ifndef atomic_mb_set
#define atomic_mb_set(ptr, i) do { \
@ -237,12 +312,6 @@
#ifndef atomic_xchg
#if defined(__clang__)
#define atomic_xchg(ptr, i) __sync_swap(ptr, i)
#elif defined(__ATOMIC_SEQ_CST)
#define atomic_xchg(ptr, i) ({ \
typeof(*ptr) _new = (i), _old; \
__atomic_exchange(ptr, &_new, &_old, __ATOMIC_SEQ_CST); \
_old; \
})
#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))
@ -266,4 +335,5 @@
#define atomic_and(ptr, n) ((void) __sync_fetch_and_and(ptr, n))
#define atomic_or(ptr, n) ((void) __sync_fetch_and_or(ptr, n))
#endif
#endif /* __ATOMIC_RELAXED */
#endif /* __QEMU_ATOMIC_H */