[Xen-devel] Memory barrier definitions in xenctrl.h for ia64?

["Daniel P. Berrange" <berrange@xxxxxxxxxx>]

Looking in tools/libxc/xenctrl.h it seems we define macros for memory barriers, 

#if defined(__i386__)
#define mb()  __asm__ __volatile__ ( "lock; addl $0,0(%%esp)" : : : "memory" )
#define rmb() __asm__ __volatile__ ( "lock; addl $0,0(%%esp)" : : : "memory" )
#define wmb() __asm__ __volatile__ ( "" : : : "memory")
#elif defined(__x86_64__)
#define mb()  __asm__ __volatile__ ( "mfence" : : : "memory")
#define rmb() __asm__ __volatile__ ( "lfence" : : : "memory")
#define wmb() __asm__ __volatile__ ( "" : : : "memory")
#elif defined(__ia64__)
/* FIXME */
#define mb()
#define rmb()
#define wmb()
#elif defined(__powerpc__)
/* XXX loosen these up later */
#define mb()   __asm__ __volatile__ ("sync" : : : "memory")
#define rmb()  __asm__ __volatile__ ("sync" : : : "memory") /* lwsync? */
#define wmb()  __asm__ __volatile__ ("sync" : : : "memory") /* eieio? */
#else
#error "Define barriers"
#endif

I'm not familiar with ia64 myself - does it really not need memory barriers?

The userspace tools blktap, xenfb & xconsoled are all using these macros in 
various places so if ia64 does indeed need memory barriers it looks like
there is some nasty bug potential here

Regards,
Dan.
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