powerpc: Add "memory" attribute for mfmsr()

commit b416c9a1 upstream.

Add "memory" attribute in inline assembly language as a compiler
barrier to make sure 4.6.x GCC don't reorder mfmsr().
Signed-off-by: Tiejun Chen <tiejun.chen@windriver.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>

arch/powerpc/include/asm/reg.h

@@ -870,7 +870,8 @@
 /* Macros for setting and retrieving special purpose registers */
 #ifndef __ASSEMBLY__
 #define mfmsr()		({unsigned long rval; \
-			asm volatile("mfmsr %0" : "=r" (rval)); rval;})
+			asm volatile("mfmsr %0" : "=r" (rval) : \
+						: "memory"); rval;})
 #ifdef CONFIG_PPC64
 #define __mtmsrd(v, l)	asm volatile("mtmsrd %0," __stringify(l) \
 				     : : "r" (v) : "memory")