[PATCH] i386: fix dubious segment register clear in cpu_init()

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@goop.org>
Signed-off-by: Andi Kleen <ak@suse.de>

diff --git a/arch/i386/kernel/cpu/common.c b/arch/i386/kernel/cpu/common.c
index 70c87de..730a7ab 100644 (file)
--- a/arch/i386/kernel/cpu/common.c
+++ b/arch/i386/kernel/cpu/common.c
@@ -675,7 +675,7 @@ old_gdt:
 #endif
 
        /* 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);