X-Git-Url: https://git.lttng.org/?p=urcu.git;a=blobdiff_plain;f=urcu%2Farch%2Fx86.h;h=7af1ca524e091fb9f9aaa8b6c2d1d102d3abe270;hp=9e5411fd4453ee7033d15e0280fdf9208d8b3f50;hb=b33e85a89e3fab8e58c8932d3d22e802de8d3ab2;hpb=9d2614f07691a813a3c560a6c0bcd0a7be854ed5

diff --git a/urcu/arch/x86.h b/urcu/arch/x86.h
index 9e5411f..7af1ca5 100644
--- a/urcu/arch/x86.h
+++ b/urcu/arch/x86.h
@@ -32,25 +32,46 @@ extern "C" {
 #define CAA_CACHE_LINE_SIZE	128
 
 #ifdef CONFIG_RCU_HAVE_FENCE
-#define cmm_mb()    asm volatile("mfence":::"memory")
-#define cmm_rmb()   asm volatile("lfence":::"memory")
-#define cmm_wmb()   asm volatile("sfence"::: "memory")
+#define cmm_mb()    __asm__ __volatile__ ("mfence":::"memory")
+
+/*
+ * Define cmm_rmb/cmm_wmb to "strict" barriers that may be needed when
+ * using SSE or working with I/O areas.  cmm_smp_rmb/cmm_smp_wmb are
+ * only compiler barriers, which is enough for general use.
+ */
+#define cmm_rmb()     __asm__ __volatile__ ("lfence":::"memory")
+#define cmm_wmb()     __asm__ __volatile__ ("sfence"::: "memory")
+#define cmm_smp_rmb() cmm_barrier()
+#define cmm_smp_wmb() cmm_barrier()
 #else
 /*
- * Some non-Intel clones support out of order store. cmm_wmb() ceases to be a
- * nop for these.
+ * We leave smp_rmb/smp_wmb as full barriers for processors that do not have
+ * fence instructions.
+ *
+ * An empty cmm_smp_rmb() may not be enough on old PentiumPro multiprocessor
+ * systems, due to an erratum.  The Linux kernel says that "Even distro
+ * kernels should think twice before enabling this", but for now let's
+ * be conservative and leave the full barrier on 32-bit processors.  Also,
+ * IDT WinChip supports weak store ordering, and the kernel may enable it
+ * under our feet; cmm_smp_wmb() ceases to be a nop for these processors.
  */
-#define cmm_mb()    asm volatile("lock; addl $0,0(%%esp)":::"memory")
-#define cmm_rmb()   asm volatile("lock; addl $0,0(%%esp)":::"memory")
-#define cmm_wmb()   asm volatile("lock; addl $0,0(%%esp)"::: "memory")
+#if (CAA_BITS_PER_LONG == 32)
+#define cmm_mb()    __asm__ __volatile__ ("lock; addl $0,0(%%esp)":::"memory")
+#define cmm_rmb()    __asm__ __volatile__ ("lock; addl $0,0(%%esp)":::"memory")
+#define cmm_wmb()    __asm__ __volatile__ ("lock; addl $0,0(%%esp)":::"memory")
+#else
+#define cmm_mb()    __asm__ __volatile__ ("lock; addl $0,0(%%rsp)":::"memory")
+#define cmm_rmb()    __asm__ __volatile__ ("lock; addl $0,0(%%rsp)":::"memory")
+#define cmm_wmb()    __asm__ __volatile__ ("lock; addl $0,0(%%rsp)":::"memory")
+#endif
 #endif
 
-#define caa_cpu_relax()	asm volatile("rep; nop" : : : "memory");
+#define caa_cpu_relax()	__asm__ __volatile__ ("rep; nop" : : : "memory");
 
 #define rdtscll(val)							  \
 	do {						  		  \
 	     unsigned int __a, __d;					  \
-	     asm volatile("rdtsc" : "=a" (__a), "=d" (__d));		  \
+	     __asm__ __volatile__ ("rdtsc" : "=a" (__a), "=d" (__d));	  \
 	     (val) = ((unsigned long long)__a)				  \
 			| (((unsigned long long)__d) << 32);		  \
 	} while(0)