Re: [PATCH v8 07/10] x86, mpx: decode MPX instruction to get bound violation information

From: Thomas Gleixner
Date: Fri Sep 12 2014 - 13:52:53 EST


On Thu, 11 Sep 2014, H. Peter Anvin wrote:

> On 09/11/2014 03:32 PM, Dave Hansen wrote:
> > On 09/11/2014 03:18 PM, Thomas Gleixner wrote:
> >> On Thu, 11 Sep 2014, Qiaowei Ren wrote:
> >>> This patch sets bound violation fields of siginfo struct in #BR
> >>> exception handler by decoding the user instruction and constructing
> >>> the faulting pointer.
> >>>
> >>> This patch does't use the generic decoder, and implements a limited
> >>> special-purpose decoder to decode MPX instructions, simply because the
> >>> generic decoder is very heavyweight not just in terms of performance
> >>> but in terms of interface -- because it has to.
> >>
> >> And why is that an argument to add another special purpose decoder?
> >
> > Peter asked for it to be done this way specifically:
> >
> > https://lkml.org/lkml/2014/6/19/411
> >
>
> Specifically because marshaling the data in and out of the generic
> decoder was more complex than a special-purpose decoder.

Well, I did not see the trainwreck which tried to use the generic
decoder, but as I explained in the other mail, there is no reason not
to use it and I can't see any complexity in retrieving the data beyond
calling insn_get_length(insn);

Thanks,

tglx
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