qemu-barrier.h

   1 #ifndef __QEMU_BARRIER_H
   2 #define __QEMU_BARRIER_H 1
   3
   4 /* Compiler barrier */
   5 #define barrier()   asm volatile("" ::: "memory")
   6
   7 #if defined(__i386__)
   8
   9 /*
  10  * Because of the strongly ordered x86 storage model, wmb() and rmb() are nops
  11  * on x86(well, a compiler barrier only).  Well, at least as long as
  12  * qemu doesn't do accesses to write-combining memory or non-temporal
  13  * load/stores from C code.
  14  */
  15 #define smp_wmb()   barrier()
  16 #define smp_rmb()   barrier()
  17 /*
  18  * We use GCC builtin if it's available, as that can use
  19  * mfence on 32 bit as well, e.g. if built with -march=pentium-m.
  20  * However, on i386, there seem to be known bugs as recently as 4.3.
  21  * */
  22 #if defined(__GNUC__) && __GNUC__ >= 4 && __GNUC_MINOR__ >= 4
  23 #define smp_mb() __sync_synchronize()
  24 #else
  25 #define smp_mb() asm volatile("lock; addl $0,0(%%esp) " ::: "memory")
  26 #endif
  27
  28 #elif defined(__x86_64__)
  29
  30 #define smp_wmb()   barrier()
  31 #define smp_rmb()   barrier()
  32 #define smp_mb() asm volatile("mfence" ::: "memory")
  33
  34 #elif defined(_ARCH_PPC)
  35
  36 /*
  37  * We use an eieio() for wmb() on powerpc.  This assumes we don't
  38  * need to order cacheable and non-cacheable stores with respect to
  39  * each other
  40  */
  41 #define smp_wmb()   asm volatile("eieio" ::: "memory")
  42
  43 #if defined(__powerpc64__)
  44 #define smp_rmb()   asm volatile("lwsync" ::: "memory")
  45 #else
  46 #define smp_rmb()   asm volatile("sync" ::: "memory")
  47 #endif
  48
  49 #define smp_mb()   asm volatile("sync" ::: "memory")
  50
  51 #else
  52
  53 /*
  54  * For (host) platforms we don't have explicit barrier definitions
  55  * for, we use the gcc __sync_synchronize() primitive to generate a
  56  * full barrier.  This should be safe on all platforms, though it may
  57  * be overkill for wmb() and rmb().
  58  */
  59 #define smp_wmb()   __sync_synchronize()
  60 #define smp_mb()   __sync_synchronize()
  61 #define smp_rmb()   __sync_synchronize()
  62
  63 #endif
  64
  65 #endif