From: "Alex Bennée" <alex.bennee@linaro.org>
To: qemu-devel@nongnu.org
Cc: pbonzini@redhat.com, sbruno@freebsd.org, peter.maydell@linaro.org
Subject: Re: [Qemu-devel] [PATCH v1 2/2] include/qemu/atomic: add compile time asserts
Date: Fri, 01 Apr 2016 16:03:01 +0100 [thread overview]
Message-ID: <87pou9fk2i.fsf@linaro.org> (raw)
In-Reply-To: <1458577386-9984-3-git-send-email-alex.bennee@linaro.org>
Alex Bennée <alex.bennee@linaro.org> writes:
> To be safely portable no atomic access should be trying to do more than
> the natural word width of the host. The most common abuse is trying to
> atomically access 64 bit values on a 32 bit host.
>
> This patch adds some QEMU_BUILD_BUG_ON to the __atomic instrinsic paths
> to create a build failure if (sizeof(*ptr) > sizeof(void *)).
>
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Ping Paolo. Is this worth including in a re-spin?
> ---
> include/qemu/atomic.h | 58 ++++++++++++++++++++++++++++++---------------------
> 1 file changed, 34 insertions(+), 24 deletions(-)
>
> diff --git a/include/qemu/atomic.h b/include/qemu/atomic.h
> index 8f1d8d9..5bc4d6c 100644
> --- a/include/qemu/atomic.h
> +++ b/include/qemu/atomic.h
> @@ -42,30 +42,34 @@
> * 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_read(ptr) \
> + ({ \
> + QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
> + 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); \
> +#define atomic_set(ptr, i) do { \
> + QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
> + 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_read(ptr) \
> + ({ \
> + QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
> + 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); \
> +#define atomic_rcu_set(ptr, i) do { \
> + QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
> + typeof(*ptr) _val = (i); \
> + __atomic_store(ptr, &_val, __ATOMIC_RELEASE); \
> } while(0)
>
> /* atomic_mb_read/set semantics map Java volatile variables. They are
> @@ -79,6 +83,7 @@
> #if defined(_ARCH_PPC)
> #define atomic_mb_read(ptr) \
> ({ \
> + QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
> typeof(*ptr) _val; \
> __atomic_load(ptr, &_val, __ATOMIC_RELAXED); \
> smp_rmb(); \
> @@ -86,22 +91,25 @@
> })
>
> #define atomic_mb_set(ptr, i) do { \
> + QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
> 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_read(ptr) \
> + ({ \
> + QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
> + 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); \
> +#define atomic_mb_set(ptr, i) do { \
> + QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
> + typeof(*ptr) _val = (i); \
> + __atomic_store(ptr, &_val, __ATOMIC_SEQ_CST); \
> } while(0)
> #endif
>
> @@ -109,6 +117,7 @@
> /* All the remaining operations are fully sequentially consistent */
>
> #define atomic_xchg(ptr, i) ({ \
> + QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
> typeof(*ptr) _new = (i), _old; \
> __atomic_exchange(ptr, &_new, &_old, __ATOMIC_SEQ_CST); \
> _old; \
> @@ -117,6 +126,7 @@
> /* Returns the eventual value, failed or not */
> #define atomic_cmpxchg(ptr, old, new) \
> ({ \
> + QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
> typeof(*ptr) _old = (old), _new = (new); \
> __atomic_compare_exchange(ptr, &_old, &_new, false, \
> __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST); \
--
Alex Bennée
next prev parent reply other threads:[~2016-04-01 15:03 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-21 16:23 [Qemu-devel] [PATCH v1 0/2] Fix for FreeBSD compile on i386 Alex Bennée
2016-03-21 16:23 ` [Qemu-devel] [PATCH v1 1/2] cpus: don't use atomic_read for vm_clock_warp_start Alex Bennée
2016-03-21 16:26 ` Paolo Bonzini
2016-03-21 17:45 ` Alex Bennée
2016-03-21 16:23 ` [Qemu-devel] [PATCH v1 2/2] include/qemu/atomic: add compile time asserts Alex Bennée
2016-04-01 15:03 ` Alex Bennée [this message]
2016-04-04 8:33 ` Paolo Bonzini
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