linux-kernel - 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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Message-ID: <20191217183135.GA3944@willie-the-truck>
Date:   Tue, 17 Dec 2019 18:31:35 +0000
From:   Will Deacon <will@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Daniel Axtens <dja@...ens.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Christophe Leroy <christophe.leroy@....fr>,
        linux-arch <linux-arch@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        Segher Boessenkool <segher@...nel.crashing.org>,
        Arnd Bergmann <arnd@...db.de>,
        Christian Borntraeger <borntraeger@...ibm.com>
Subject: Re: READ_ONCE() + STACKPROTECTOR_STRONG == :/ (was Re: [GIT PULL]
 Please pull powerpc/linux.git powerpc-5.5-2 tag (topic/kasan-bitops))

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@...ux-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