Index: compiler.h
===================================================================
RCS file: /cvsroot/xsrc/xfree/xc/programs/Xserver/hw/xfree86/common/compiler.h,v
retrieving revision 1.20
diff -u -r1.20 compiler.h
--- compiler.h	8 Apr 2005 20:56:22 -0000	1.20
+++ compiler.h	1 Oct 2006 15:19:38 -0000
@@ -1357,8 +1357,15 @@
 #    define stq_u(v,p)	(*(unsigned long  *)(p)) = (v)
 #    define stl_u(v,p)	(*(unsigned int   *)(p)) = (v)
 #    define stw_u(v,p)	(*(unsigned short *)(p)) = (v)
-#    define mem_barrier()   /* NOP */
-#    define write_mem_barrier()   /* NOP */
+#    if defined(__NetBSD__) && defined(__amd64__)
+#     define mem_barrier() \
+       __asm__ __volatile__ ("lock; addl $0,0(%%rsp)": : :"memory")
+#     define write_mem_barrier() \
+       __asm__ __volatile__ ("": : :"memory")
+#    else
+#     define mem_barrier()   /* NOP */
+#     define write_mem_barrier()   /* NOP */
+#    endif
 
 #    if !defined(__SUNPRO_C)
 #    if !defined(FAKEIT) && !defined(__mc68000__) && !defined(__arm__) && !defined(__sh__) && !defined(__hppa__)