mb
#define mb() __asm__ volatile("mb" : : : "memory")
#define mb() __asm volatile("lock; addl $0,-4(%%esp)" : : : "memory", "cc")
#define mb() __membar("mfence")
#define mb() __membar("dsb sy")
#define mb() __membar("dsb sy")
#define mb() mips_sync()
#define mb() __membar("sync")
#define mb() __membar("sync")
#define mb() __membar("fence iorw,iorw")
#define mb() membar_sync()