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

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Date:	Sat, 27 Feb 2016 11:16:44 -0800
From:	Dave Hansen <dave@...1.net>
To:	Ingo Molnar <mingo@...nel.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>
Cc:	"H. Peter Anvin" <hpa@...or.com>, 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 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?