x86: introduce __ASM_REG macro.

There are situations in which the architecture wants to use the
register that represents its word-size, whatever it is. For those,
introduce __ASM_REG in asm.h, along with the first users _ASM_AX
and _ASM_DX. They have users waiting for it, namely the getuser
functions.

Signed-off-by: Glauber Costa <gcosta@redhat.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/asm-x86/asm.h b/include/asm-x86/asm.h
index 70939820..435402e 100644
--- a/include/asm-x86/asm.h
+++ b/include/asm-x86/asm.h
@@ -14,6 +14,7 @@
 #endif
 
 #define __ASM_SIZE(inst)	__ASM_SEL(inst##l, inst##q)
+#define __ASM_REG(reg)		__ASM_SEL(e##reg, r##reg)
 
 #define _ASM_PTR	__ASM_SEL(.long, .quad)
 #define _ASM_ALIGN	__ASM_SEL(.balign 4, .balign 8)
@@ -24,6 +25,8 @@
 #define _ASM_ADD	__ASM_SIZE(add)
 #define _ASM_SUB	__ASM_SIZE(sub)
 #define _ASM_XADD	__ASM_SIZE(xadd)
+#define _ASM_AX		__ASM_REG(ax)
+#define _ASM_DX		__ASM_REG(dx)
 
 /* Exception table entry */
 # define _ASM_EXTABLE(from,to) \