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

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Message-ID: <54AAFFA3.6000901@linux.intel.com>
Date:	Mon, 05 Jan 2015 13:18:27 -0800
From:	Dave Hansen <dave.hansen@...ux.intel.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Andy Lutomirski <luto@...capital.net>,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 3.19 3/3] x86, mpx: Change the MPX enable/disable API
 to arch_prctl

On 01/05/2015 12:42 PM, Andi Kleen wrote:
> Dave Hansen <dave.hansen@...ux.intel.com> writes:
>> On 12/29/2014 04:52 PM, Andy Lutomirski wrote:
>>> This has the benefit the it avoids cluttering prctl with more
>>> arch-specific functionality.  The down side is that arch_prctl will
>>> need to be wired up as a 32-bit syscall to add 32-bit support for
>>> MPX.
>>
>> There is existing userspace out there which depends on the existing
>> prctl() setup.  There isn't a _lot_ and it might still be able to be
>> changed easily, but this isn't a given.
>>
>> I'll check in with the folks doing the gcc (runtime) part of this next
>> week and see what they think.
> 
> It'll be quite messy for 32bit because they would need to use syscall(),
> as glibc won't have a arch_prctl stub.

Yeah, I'd _really_ prefer not to change it.  The code is in a gcc
branch, but is getting pulled in to the 5.0 release.  We've got
*absolutely* no shortage of prctl numbers.
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