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

From: H. Peter Anvin
Date: Sat Feb 27 2016 - 14:36:12 EST

On February 27, 2016 11:16:44 AM PST, Dave Hansen <dave@xxxxxxxx> wrote:
>On 02/27/2016 03:41 AM, Ingo Molnar wrote:
>> * Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> wrote:
>>> > On Fri, 26 Feb 2016 09:44:00 -0800 "H. Peter Anvin"
><hpa@xxxxxxxxx> 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
>>> > alignment of the enclosing unions on (some) 32 bit platforms and
>>> > 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
>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
>How should we get Stephen's patch in to the tip tree?

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