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Date: Tue, 17 Dec 2019 18:31:35 +0000
From: Will Deacon <will@kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: READ_ONCE() + STACKPROTECTOR_STRONG == :/ (was Re: [GIT PULL]
 Please pull powerpc/linux.git powerpc-5.5-2 tag (topic/kasan-bitops))
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Cc: linux-arch <linux-arch@vger.kernel.org>, Arnd Bergmann <arnd@arndb.de>,
 Peter Zijlstra <peterz@infradead.org>,
 Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
 Christian Borntraeger <borntraeger@de.ibm.com>,
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 linuxppc-dev <linuxppc-dev@lists.ozlabs.org>, Daniel Axtens <dja@axtens.net>
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On Tue, Dec 17, 2019 at 10:05:53AM -0800, Linus Torvalds wrote:
> On Tue, Dec 17, 2019 at 10:04 AM Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> >
> > Let me think about it.
> 
> .. and in the short term, maybe for code generation, the right thing
> is to just do the cast in the bitops, where we can just cast to
> "unsigned long *" and remove the volatile that way.

Yeah, I think I'll spin that patch series tomorrow anyway, since I don't
think we need to hold it up.

> I'm still hoping there's a trick, but..

Well, there's always Peter's awful hack [1] but it's really gross. FWIW,
I've pushed the handful of patches I have to [2], which drop the GCC 4.8
workaround and introduce a non-atomic version instead of the
'__builtin_memcpy()'.

Will

[1] https://lore.kernel.org/lkml/20191213125618.GD2844@hirez.programming.kicks-ass.net
[2] https://git.kernel.org/pub/scm/linux/kernel/git/will/linux.git/log/?h=rwonce/cleanup