[PATCH] fix dubious segment register clear in cpu_init()

From: Jeremy Fitzhardinge
Date: Thu Aug 03 2006 - 19:46:51 EST

Fix a very dubious piece of code in
arch/i386/kernel/cpu/common.c:cpu_init(). This clears out %fs and
%gs, but clobbers %eax in the process without telling gcc. It turns
out that gcc happens to be not using %eax at that point anyway so it
doesn't matter much, but it looks like a bomb waiting to go off.

This does end up saving an instruction, because gcc wants %eax==0 for
the set_debugreg()s below.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xxxxxxxx>

diff -r ced3124154dc arch/i386/kernel/cpu/common.c
--- a/arch/i386/kernel/cpu/common.c Mon Jul 31 18:52:19 2006 -0700
+++ b/arch/i386/kernel/cpu/common.c Thu Aug 03 16:23:02 2006 -0700
@@ -675,7 +675,7 @@ old_gdt:

/* Clear %fs and %gs. */
- asm volatile ("xorl %eax, %eax; movl %eax, %fs; movl %eax, %gs");
+ asm volatile ("movl %0, %%fs; movl %0, %%gs" : : "r" (0));

/* Clear all 6 debug registers: */
set_debugreg(0, 0);

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