On Thu, 17 Jul 2003, Davide Libenzi wrote:
> On Thu, 17 Jul 2003, Randy.Dunlap wrote:
>
> >
> > In arch/i386/kernel, inline asm for loading IDT (lidt) is used a few
> > times, but with slightly different constraints and output/input
> > definitions. Are these OK, equivalent, or what?
> >
> > [rddunlap@dragon kernel]$ findc lidt
> > ./cpu/common.c:484: __asm__ __volatile__("lidt %0": "=m" (idt_descr));
> > ./traps.c:783: __asm__ __volatile__("lidt %0": "=m" (idt_descr));
> >
> > vs.
> >
> > ./reboot.c:186: __asm__ __volatile__ ("lidt %0" : : "m" (real_mode_idt));
> > ./reboot.c:261: __asm__ __volatile__("lidt %0": :"m" (no_idt));
> > ./suspend.c:95: asm volatile ("lidt %0" :: "m" (saved_context.idt_limit));
>
> I'd have said no looking at the syntax (input/output), but they indeed
> generate the same code (just checked).
Randy, I'd say that this :
__asm__ __volatile__("lidt %0": "=m" (var));
is better then :
__asm__ __volatile__("lidt %0": :"m" (var));
IMHO, since "var" is really an output parameter.
- Davide
-
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This archive was generated by hypermail 2b29 : Wed Jul 23 2003 - 22:00:31 EST