linux-kernel - Re: [tip:mm/pkeys] mm/pkeys: Fix siginfo ABI breakage caused by new u64 field

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Message-ID: <CA+55aFztVgS-GQQ=vqZU9eq9X+AprnNim-twbitwjQ_d797j+w@mail.gmail.com>
Date:	Sun, 6 Mar 2016 10:45:23 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Peter Anvin <hpa@...or.com>, Dave Hansen <dave@...1.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Helge Deller <deller@....de>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:mm/pkeys] mm/pkeys: Fix siginfo ABI breakage caused by new
 u64 field

On Sat, Mar 5, 2016 at 8:52 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Sat, Mar 05, 2016 at 02:50:06PM +0100, Ingo Molnar wrote:
>> A more workable method would be to have a test .c file that includes all UAPI
>> structures in existence and defines a variable out of every single one, and then
>> generates a list of sizeof() values or so. But even that isn't perfect: a
>> structure might shift some fields forward, into a pre-existing hole, without
>> changing the sizeof? We'd need a list of all field offsets in all structures to be
>> really sure, and that's nasty.
>
> pahole has such logic, right?

sparse could be taught to warn about unaligned u64's, but there are
still config issues and issues across other architectures, and if some
case gets missed it can be really quite painful.

          Linus