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Re: [Xen-devel] [PATCH] PVH: vcpu info placement, load selectors, and remove debug printk.

>>> On 04.06.13 at 02:43, Mukesh Rathor <mukesh.rathor@xxxxxxxxxx> wrote:
> @@ -1327,6 +1329,18 @@ static void __init xen_setup_stackprotector(void)
>       /* PVH TBD/FIXME: investigate setup_stack_canary_segment */
>       if (xen_feature(XENFEAT_auto_translated_physmap)) {
>               switch_to_new_gdt(0);
> +
> +             /* xen started us with null selectors. load them now */
> +             __asm__ __volatile__ (
> +                     "movl %0,%%ds\n"
> +                     "movl %0,%%ss\n"
> +                     "pushq %%rax\n"
> +                     "leaq 1f(%%rip),%%rax\n"
> +                     "pushq %%rax\n"
> +                     "retfq\n"
> +                     "1:\n"
> +                     : : "r" (__KERNEL_DS), "a" (__KERNEL_CS) : "memory");
> +

I can see why you want CS to be reloaded (and CS, other than the
comment says, clearly hasn't been holding a null selector up to here.

I can't immediately see why you'd need SS to be other than null, and
it completely escapes me why you'd need to DS (but not ES) to be

Furthermore, is there any reason why you use "retfq" (Intel syntax)
when all assembly code otherwise uses AT&T syntax (the proper
equivalent here would be "lretq")?

And finally, please consistently use %<number> (which, once
fixed, will make clear that the second constraint really can be "r"),
and avoid using suffixes on moves to/from selector registers
(which, once fixed, will make clear that at least the first constraint
really can be relaxed to "rm").


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