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 <[e-mail]>
Looks-okay-to: Pavel Machek <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>
Cc: Len Brown <[e-mail]>
Acked-by: Andi Kleen <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/i386/kernel/acpi/wakeup.S

···
 #
 ENTRY(acpi_copy_wakeup_routine)
 
+	pushl	%ebx
 	sgdt	saved_gdt
 	sidt	saved_idt
 	sldt	saved_ldt
···
 	movl	%edx, video_flags - wakeup_start (%eax)
 	movl	$0x12345678, real_magic - wakeup_start (%eax)
 	movl	$0x12345678, saved_magic
+	popl	%ebx
 	ret
 
 save_registers: