linux-kernel - x86: asm doubt

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Date:	Sun, 15 Mar 2009 11:16:24 -0300
From:	Sergio Luis <eeeesti@...il.com>
To:	Ingo Molnar <mingo@...e.hu>, "Rafael J. Wysocki" <rjw@...k.pl>,
	Pavel Machek <pavel@...e.cz>,
	Linux-kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: x86: asm doubt

Hi there,

taking a look at arch/x86/power/cpu_(32|64).c, I saw the 32.c one
using the following macros

#define savesegment(seg, value)                         \
        asm("mov %%" #seg ",%0":"=r" (value) : : "memory")


#define loadsegment(seg, value)                 \
        asm volatile("\n"                       \
                     "1:\t"                     \
                     "movl %k0,%%" #seg "\n"    \
                     "2:\n"                     \
                     ".section .fixup,\"ax\"\n" \
                     "3:\t"                     \
                     "movl %k1, %%" #seg "\n\t" \
                     "jmp 2b\n"                 \
                     ".previous\n"              \
                     _ASM_EXTABLE(1b,3b)        \
                     : :"r" (value), "r" (0) : "memory")


saving and loading segment registers as in

savesegment(es, ctxt->es);
loadsegment(es, ctxt->es);

the code in cpu_64.c doesn't make use of such macros, doing the following:

saving:
 asm volatile ("movw %%es, %0" : "=m" (ctxt->es));

loading:
asm volatile ("movw %0, %%es" :: "r" (ctxt->es));

So, my question is... what's the actual difference between both
versions? Aren't the macros suitable for the 64 version as well?

Thanks,
Sergio.
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