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SubjectRe: [x86] do_arch_prctl
Eric Lacombe wrote:
> Thanks for your answer, I've got one last question ;)
> In the ARCH_GET_GS, can you explain the line 834 to 838?
>
> In fact, at first sight I thought that just the line 836 was sufficient, but I
> obviously miss the case where MSR_KERNEL_GS_BASE does not reflect the value
> requested, hence my question.
>

I think the rationale is that rdmsr is slow, so reading the value from
the task context is faster where possible.

It's not a very pretty part of the architecture :/

J

> 828 case ARCH_GET_GS: {
> 829 unsigned long base;
> 830 unsigned gsindex;
> 831 if (task->thread.gsindex == GS_TLS_SEL)
> 832 base = read_32bit_tls(task, GS_TLS);
> 833 else if (doit) {
> 834 asm("movl %%gs,%0" : "=r" (gsindex));
> 835 if (gsindex)
> 836 rdmsrl(MSR_KERNEL_GS_BASE, base);
> 837 else
> 838 base = task->thread.gs;
> 839 }
> 840 else
> 841 base = task->thread.gs;
>
> Thanks,
>
> Eric
>
>
>



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