linux-kernel - Re: [PATCH] x86, pkeys: fix siginfo ABI breakage from new field

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Message-ID: <9E8119F8-1F37-4084-AE31-34CA6DE8C15E@zytor.com>
Date:	Sat, 27 Feb 2016 11:35:08 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Dave Hansen <dave@...1.net>, Ingo Molnar <mingo@...nel.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>
CC:	linux-kernel@...r.kernel.org, dave.hansen@...ux.intel.com,
	akpm@...ux-foundation.org, tglx@...utronix.de, mingo@...e.hu,
	peterz@...radead.org, linux-next@...r.kernel.org, deller@....de
Subject: Re: [PATCH] x86, pkeys: fix siginfo ABI breakage from new field

On February 27, 2016 11:16:44 AM PST, Dave Hansen <dave@...1.net> wrote:
>On 02/27/2016 03:41 AM, Ingo Molnar wrote:
>> * Stephen Rothwell <sfr@...b.auug.org.au> wrote:
>>> > On Fri, 26 Feb 2016 09:44:00 -0800 "H. Peter Anvin"
><hpa@...or.com> wrote:
>>>> > > __u64 is okay, "unsigned long" is really messy in the presence
>of 32-on-64 bit ABIs...
>>> > 
>>> > Yeah, but unfortunately, any 64 bit scalar type here will change
>the
>>> > alignment of the enclosing unions on (some) 32 bit platforms and
>thus
>>> > break the ABI.
>> Then a different solution has to be found.
>
>I've acked Stephen's initial patch changing the 'u64' to an 'int'.  x86
>only needs 4 bits, and in the remote chance that a future
>implementation
>needed more space, we could easily add a second 32-bit field "_pkey_hi"
>or something that wouldn't have the alignment issues of a true 64-bit
>type.
>
>How should we get Stephen's patch in to the tip tree?

u32?
-- 
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