linux-kernel - Re: [PATCH 3.19 3/3] x86, mpx: Change the MPX enable/disable API to arch

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Date:	Tue, 06 Jan 2015 10:30:09 -0800
From:	Dave Hansen <dave.hansen@...ux.intel.com>
To:	Andy Lutomirski <luto@...capital.net>
CC:	Andi Kleen <andi@...stfloor.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
	ilya.enkovich@...el.com
Subject: Re: [PATCH 3.19 3/3] x86, mpx: Change the MPX enable/disable API
 to arch_prctl

On 01/06/2015 10:06 AM, Andy Lutomirski wrote:
> On Tue, Jan 6, 2015 at 9:48 AM, Dave Hansen <dave.hansen@...ux.intel.com> wrote:
>> On 01/05/2015 09:59 PM, Andy Lutomirski wrote:
>>> But I decided to check whether libmpx links against glibc, and I can't
>>> find sources for it at all.  Do they exist?  Is there any code with
>>> source available that invokes this prctl?
>>>
>>> If not, I personally have very little sympathy for the argument that a
>>> binary buried in the depths of the Intel SDE would need to change if
>>> we switched to using arch_prctl.  And I think that it should issue the
>>> syscall itself without using glibc, in which case the syscall wrapper
>>> issue is moot.
>>
>> Andy, as I mentioned previously, there is code in a GCC branch that uses
>> the existing prctl().  It's also been posted for review to one of the
>> GCC mailing lists.  I've been told that it will be in gcc 5.0.
> 
> Can you point me to it?  I found the code generation stuff in the gcc
> branch, but I couldn't find the runtime.

cc'ing Ilya who is working on the gcc parts...

Ilya, is the MPX runtime that uses the prctl() calls available somewhere
publicly that it can be grabbed?

I couldn't find it in GCC SVN anywhere.

>> The Intel SDE does not use the prctl() in any way that I know of.
> 
> I found a couple references suggesting that libmpx lived in the SDE.
> For example:
> 
> https://software.intel.com/en-us/articles/using-intel-mpx-with-the-intel-software-development-emulator

Andy, I think you're mistaken.  The SDE allows you to run MPX code on a
system without MPX support in hardware.  It does not, itself, provide
MPX code.  The references you see there are to a runtime library that
you obtain separately from the SDE.  You run the library _under_ the SDE.

I hope this clears things up.
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