linux-kernel - Re: [PATCH] [v4] x86, pkeys: fix siginfo ABI breakage from new field

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Date:	Thu, 3 Mar 2016 16:41:04 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Dave Hansen <dave@...1.net>
Cc:	linux-kernel@...r.kernel.org, dave.hansen@...ux.intel.com,
	sfr@...b.auug.org.au, akpm@...ux-foundation.org,
	tglx@...utronix.de, mingo@...e.hu, hpa@...or.com,
	peterz@...radead.org, linux-next@...r.kernel.org, deller@....de
Subject: Re: [PATCH] [v4] x86, pkeys: fix siginfo ABI breakage from new field


* Dave Hansen <dave@...1.net> wrote:

> To fix this, we replace the u64 with an '__u32'.  The __u32 is guaranteed to 
> union well with the pointers from _addr_bnd.  It is also plenty large enough to 
> store the 16-bit pkey we have today on x86.

The 'union well' sentence is really a leftover from the earlier changelog (the 
problem was never about interaction between union members) - a better explantion 
is:

> To fix this, we replace the u64 with an '__u32'.  The __u32 does not change the 
> minimum alignment requirements of the structure and it is also plenty large 
> enough to store the 16-bit pkey we have today on x86.

I fixed this up locally, no need to resend.

Thanks,

	Ingo