Messages in this thread | | | Date | Thu, 17 Jul 2003 16:18:06 -0700 (PDT) | From | Davide Libenzi <> | Subject | Re: asm (lidt) question |
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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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