[PATCH for review] [115/145] x86_64: fix dubious segment register clear in cpu_init()

Andi Kleen
2006-08-10T19:48:10Z

r

From: Jeremy Fitzhardinge <jeremy@goop.org>

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>

---
arch/i386/kernel/cpu/common.c | 2 +-
1 files changed, 1 insertion(+), 1 deletion(-)

Index: linux/arch/i386/kernel/cpu/common.c
===================================================================
--- linux.orig/arch/i386/kernel/cpu/common.c
+++ linux/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);