linux-kernel - Re: [RFC][PATCH 0/8] x86, mpx: Support 32-bit binaries on 64-bit kernels

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Date:	Fri, 12 Dec 2014 12:48:49 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Dave Hansen <dave@...1.net>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>, X86 ML <x86@...nel.org>
Subject: Re: [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@...1.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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