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Re: [Xen-devel] [PATCH] xen/arm: Fix ARM build following c/s 11c397c

Hi Andrew,

On 08/02/17 19:10, Andrew Cooper wrote:
c/s 11c397c broke the ARM build by introducing a common ACCESS_ONCE() which is
different to the definiton in smmu.c

The SMMU code included a scalar typecheck, which is worth keeping in the
common case, given ACCESS_ONCE()'s restrictions.  However, express the
typecheck differently so as to avoid Coverity compliants about unused



OOI, the variable is marked as "__maybe_unused", so why Coverity would complaint?

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Acked-by: Julien Grall <julien.grall@xxxxxxx>


CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: Julien Grall <julien.grall@xxxxxxx>
 xen/drivers/passthrough/arm/smmu.c | 10 ----------
 xen/include/xen/lib.h              |  5 ++++-
 2 files changed, 4 insertions(+), 11 deletions(-)

diff --git a/xen/drivers/passthrough/arm/smmu.c 
index cf8b8b8..06c0a45 100644
--- a/xen/drivers/passthrough/arm/smmu.c
+++ b/xen/drivers/passthrough/arm/smmu.c
@@ -198,16 +198,6 @@ typedef paddr_t phys_addr_t;

 #define VA_BITS                0       /* Only used for configuring stage-1 
input size */

-/* The macro ACCESS_ONCE start to be replaced in Linux in favor of
- * {READ, WRITE}_ONCE. Rather than introducing in the common code, keep a
- * version here. We will have to drop it when the SMMU code in Linux will
- * switch to {READ, WRITE}_ONCE.
- */
-#define __ACCESS_ONCE(x) ({ \
-        __maybe_unused typeof(x) __var = 0; \
-       (volatile typeof(x) *)&(x); })
-#define ACCESS_ONCE(x) (*__ACCESS_ONCE(x))
 #define MODULE_DEVICE_TABLE(type, name)
 #define module_param_named(name, value, type, perm)
 #define MODULE_PARM_DESC(_parm, desc)
diff --git a/xen/include/xen/lib.h b/xen/include/xen/lib.h
index 1976e4b..995a85a 100644
--- a/xen/include/xen/lib.h
+++ b/xen/include/xen/lib.h
@@ -56,7 +56,10 @@

 #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]) + __must_be_array(x))

-#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))
+#define __ACCESS_ONCE(x) ({                             \
+            (void)(typeof(x))0; /* Scalar typecheck. */ \
+            (volatile typeof(x) *)&(x); })
+#define ACCESS_ONCE(x) (*__ACCESS_ONCE(x))

 #define MASK_EXTR(v, m) (((v) & (m)) / ((m) & -(m)))
 #define MASK_INSR(v, m) (((v) * ((m) & -(m))) & (m))

Julien Grall

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