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SubjectRe: [PATCH 14/15] x86/fsgsbase/64: Support legacy behavior when FS/GS updated by ptracer
On Wed, Mar 21, 2018 at 3:11 PM, Bae, Chang Seok
<chang.seok.bae@intel.com> wrote:
> On 3/20/18, 17:47, "Andy Lutomirski" <luto@kernel.org> wrote:
>> If I've understood all your emails right, when you looked at existing
>> ptrace users, you found that all of them that write to gs and/or
>> gs_base do it as part of a putregs call that writes them at the same
>> time. If so, then your patch does exactly the same thing that my old
>> patches did, but your patch is much more complicated. So why did you
>> add all that complexity?
>
> What is tried to be provided is backward compatibility by emulating
> “mov gs (fs) …” when index is only changed and preserve a (given) base value
> in other cases.

mov to gs changes GSBASE even if GS was unchanged.

But it's not clear to me that you've identified any case where
emulating this behavior is useful.

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