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SubjectRe: [RFC][PATCH 0/8] x86, mpx: Support 32-bit binaries on 64-bit kernels
On Fri, Dec 12, 2014 at 12:27 PM, Dave Hansen <dave@sr71.net> wrote:
> On 12/12/2014 12:22 PM, Andy Lutomirski wrote:
>> On 12/12/2014 11:12 AM, Dave Hansen wrote:
>>> This is 3.20 material. I'm hoping to get some comments early
>>> in case folks have some issues with the way it's being done.
>>>
>>> The MPX hardware structures differ in layout in 32 and 64-bit
>>> mode. A 32-bit binary running on a 64-bit kernel needs the
>>> 32-bit structures, so we need code which switches between
>>> the two modes.
>>
>> The OS community figured out years ago that you aren't supposed to do
>> this. Did everyone forget to tell the hardware people?
>
> What is your concern with it, exactly?
>
> You want the same size structures with the same format for 32-bit and
> 64-bit modes?

Yes. Especially because programs can switch between 32-bit and 64-bit
mode entirely in userspace. I don't know whether any do in practice,
but programs *can*.

Or better yet: Intel could have skipped supporting it at all in 32-bit
mode. Isn't mpx somewhat of an address space hog anyway?

--Andy

--
Andy Lutomirski
AMA Capital Management, LLC


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