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Date: Thu, 5 Apr 2018 09:08:10 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: James Y Knight <jyknight@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	gregkh@linuxfoundation.org,
	Nick Desaulniers <ndesaulniers@google.com>, mka@chromium.org,
	Ingo Molnar <mingo@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	tglx@linutronix.de, Andrew Morton <akpm@linux-foundation.org>,
	Chandler Carruth <chandlerc@google.com>,
	Stephen Hines <srhines@google.com>, Kees Cook <keescook@google.com>,
	groeck@chromium.org, Greg Hackmann <ghackmann@google.com>
Subject: Re: [GIT PULL] x86/build changes for v4.17
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On Wed, Apr 04, 2018 at 10:21:05PM +0000, James Y Knight wrote:
> But allowing random pointer arithmetic, and pointer arithmetic wraparound,
> is still different than asserting that an object _field access_ can
> overflow. Clang does not believe that can happen -- it assumes that an
> object will still be contiguous. And that's why the llist stuff used to be
> broken, before it was corrected to do simply do math on a uintptr_t (which
> is a nice and simple and sane fix!).

That 'fix' wasn't anything simple, I recently ran into that
member_address_is_nonnull() trainwreck and had to think real hard wtf it
was about.