[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>

[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>
Jeremy Fitzhardinge · Andi Kleen
1 parent 3b8d1fe0f2
Showing 1 changed file with 1 additions and 1 deletions Side-by-side Diff
arch/i386/kernel/cpu/common.c
@@ -675,7 +675,7 @@
 #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);
...	...	@@ -675,7 +675,7 @@
675	675	#endif
676	676
677	677	/* Clear %fs and %gs. */
678		- asm volatile ("xorl %eax, %eax; movl %eax, %fs; movl %eax, %gs");
	678	+ asm volatile ("movl %0, %%fs; movl %0, %%gs" : : "r" (0));
679	679
680	680	/* Clear all 6 debug registers: */
681	681	set_debugreg(0, 0);