ACPI: preserve the ebx value in acpi_copy_wakeup_routine

Register %ebx serves as the "global offset table base register" for
position-independent code.  For absolute code, %ebx serves as a local
register and has no specified role in the function calling sequence.  In
either case, a function must preserve the register value for the caller.

acpi_copy_wakeup_routine overrides %ebx without saving it, this may corrupt
the called data.

Kevin found that most time the value of Sx is saved in %esi, however
sometimes compiler also uses %ebx.  When this happens, suspends fails since
sleep value in ebx is changed by acpi_copy_wakeup_routine.

The same funtion in X86_64 doesn't have this problem.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Looks-okay-to: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Len Brown <lenb@kernel.org>
Acked-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/i386/kernel/acpi/wakeup.S

@@ -230,6 +230,7 @@ bogus_magic:
 #
 ENTRY(acpi_copy_wakeup_routine)
 
+	pushl	%ebx
 	sgdt	saved_gdt
 	sidt	saved_idt
 	sldt	saved_ldt
@@ -263,6 +264,7 @@ ENTRY(acpi_copy_wakeup_routine)
 	movl	%edx, video_flags - wakeup_start (%eax)
 	movl	$0x12345678, real_magic - wakeup_start (%eax)
 	movl	$0x12345678, saved_magic
+	popl	%ebx
 	ret
 
 save_registers: