include/qemu/atomic.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 "qemu/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 /*
  21  * We use GCC builtin if it's available, as that can use
  22  * mfence on 32 bit as well, e.g. if built with -march=pentium-m.
  23  * However, on i386, there seem to be known bugs as recently as 4.3.
  24  * */
  25 #if QEMU_GNUC_PREREQ(4, 4)
  26 #define smp_mb() __sync_synchronize()
  27 #else
  28 #define smp_mb() asm volatile("lock; addl $0,0(%%esp) " ::: "memory")
  29 #endif
  30
  31 #elif defined(__x86_64__)
  32
  33 #define smp_wmb()   barrier()
  34 #define smp_rmb()   barrier()
  35 #define smp_mb() asm volatile("mfence" ::: "memory")
  36
  37 #elif defined(_ARCH_PPC)
  38
  39 /*
  40  * We use an eieio() for wmb() on powerpc.  This assumes we don't
  41  * need to order cacheable and non-cacheable stores with respect to
  42  * each other
  43  */
  44 #define smp_wmb()   asm volatile("eieio" ::: "memory")
  45
  46 #if defined(__powerpc64__)
  47 #define smp_rmb()   asm volatile("lwsync" ::: "memory")
  48 #else
  49 #define smp_rmb()   asm volatile("sync" ::: "memory")
  50 #endif
  51
  52 #define smp_mb()   asm volatile("sync" ::: "memory")
  53
  54 #else
  55
  56 /*
  57  * For (host) platforms we don't have explicit barrier definitions
  58  * for, we use the gcc __sync_synchronize() primitive to generate a
  59  * full barrier.  This should be safe on all platforms, though it may
  60  * be overkill for wmb() and rmb().
  61  */
  62 #define smp_wmb()   __sync_synchronize()
  63 #define smp_mb()   __sync_synchronize()
  64 #define smp_rmb()   __sync_synchronize()
  65
  66 #endif
  67
  68 #endif