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 #include "compiler.h"        /* QEMU_GNUC_PREREQ */
  10
  11 /*
  12  * Because of the strongly ordered x86 storage model, wmb() and rmb() are nops
  13  * on x86(well, a compiler barrier only).  Well, at least as long as
  14  * qemu doesn't do accesses to write-combining memory or non-temporal
  15  * load/stores from C code.
  16  */
  17 #define smp_wmb()   barrier()
  18 #define smp_rmb()   barrier()
  19 /*
  20  * We use GCC builtin if it's available, as that can use
  21  * mfence on 32 bit as well, e.g. if built with -march=pentium-m.
  22  * However, on i386, there seem to be known bugs as recently as 4.3.
  23  * */
  24 #if QEMU_GNUC_PREREQ(4, 4)
  25 #define smp_mb() __sync_synchronize()
  26 #else
  27 #define smp_mb() asm volatile("lock; addl $0,0(%%esp) " ::: "memory")
  28 #endif
  29
  30 #elif defined(__x86_64__)
  31
  32 #define smp_wmb()   barrier()
  33 #define smp_rmb()   barrier()
  34 #define smp_mb() asm volatile("mfence" ::: "memory")
  35
  36 #elif defined(_ARCH_PPC)
  37
  38 /*
  39  * We use an eieio() for wmb() on powerpc.  This assumes we don't
  40  * need to order cacheable and non-cacheable stores with respect to
  41  * each other
  42  */
  43 #define smp_wmb()   asm volatile("eieio" ::: "memory")
  44
  45 #if defined(__powerpc64__)
  46 #define smp_rmb()   asm volatile("lwsync" ::: "memory")
  47 #else
  48 #define smp_rmb()   asm volatile("sync" ::: "memory")
  49 #endif
  50
  51 #define smp_mb()   asm volatile("sync" ::: "memory")
  52
  53 #else
  54
  55 /*
  56  * For (host) platforms we don't have explicit barrier definitions
  57  * for, we use the gcc __sync_synchronize() primitive to generate a
  58  * full barrier.  This should be safe on all platforms, though it may
  59  * be overkill for wmb() and rmb().
  60  */
  61 #define smp_wmb()   __sync_synchronize()
  62 #define smp_mb()   __sync_synchronize()
  63 #define smp_rmb()   __sync_synchronize()
  64
  65 #endif
  66
  67 #endif