From: Linus Torvalds <torvalds@linux-foundation.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>,
Michael Ellerman <mpe@ellerman.id.au>,
dja@axtens.net,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linuxppc-dev@lists.ozlabs.org,
Christophe Leroy <christophe.leroy@c-s.fr>,
linux-arch <linux-arch@vger.kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Segher Boessenkool <segher@kernel.crashing.org>,
Arnd Bergmann <arnd@arndb.de>,
Christian Borntraeger <borntraeger@de.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))
Date: Thu, 12 Dec 2019 09:41:32 -0800 [thread overview]
Message-ID: <CAHk-=wjUBsH0BYDBv=q36482G-U7c=9bC89L_BViSciTfb8fhA@mail.gmail.com> (raw)
In-Reply-To: <20191212104610.GW2827@hirez.programming.kicks-ass.net>
On Thu, Dec 12, 2019 at 2:46 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> +#ifdef GCC_VERSION < 40800
Where does that 4.8 version check come from, and why?
Yeah, I know, but this really wants a comment. Sadly it looks like gcc
bugzilla is down, so
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145
currently gives an "Internal Server Error" for me.
[ Delete the horrid code we have because of gcc bugs ]
> +#else /* GCC_VERSION < 40800 */
> +
> +#define READ_ONCE_NOCHECK(x) \
> +({ \
> + typeof(x) __x = *(volatile typeof(x))&(x); \
I think we can/should just do this unconditionally if it helps th eissue.
Maybe add a warning about how gcc < 4.8 might mis-compile the kernel -
those versions are getting close to being unacceptable for kernel
builds anyway.
We could also look at being stricter for the normal READ/WRITE_ONCE(),
and require that they are
(a) regular integer types
(b) fit in an atomic word
We actually did (b) for a while, until we noticed that we do it on
loff_t's etc and relaxed the rules. But maybe we could have a
"non-atomic" version of READ/WRITE_ONCE() that is used for the
questionable cases?
Linus
next prev parent reply other threads:[~2019-12-12 17:41 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-06 12:46 [GIT PULL] Please pull powerpc/linux.git powerpc-5.5-2 tag (topic/kasan-bitops) Michael Ellerman
2019-12-06 13:16 ` Peter Zijlstra
2019-12-10 5:38 ` Michael Ellerman
2019-12-10 10:15 ` Peter Zijlstra
2019-12-11 0:29 ` Michael Ellerman
2019-12-12 5:42 ` READ_ONCE() + STACKPROTECTOR_STRONG == :/ (was Re: [GIT PULL] Please pull powerpc/linux.git powerpc-5.5-2 tag (topic/kasan-bitops)) Michael Ellerman
2019-12-12 8:01 ` Peter Zijlstra
2019-12-12 10:07 ` Will Deacon
2019-12-12 10:46 ` Peter Zijlstra
2019-12-12 17:04 ` Will Deacon
2019-12-12 17:16 ` Will Deacon
2019-12-12 17:41 ` Linus Torvalds [this message]
2019-12-12 17:50 ` Segher Boessenkool
2019-12-12 18:06 ` Will Deacon
2019-12-12 18:29 ` Christian Borntraeger
2019-12-12 18:43 ` Linus Torvalds
2019-12-12 19:34 ` Will Deacon
2019-12-12 20:21 ` Peter Zijlstra
2019-12-12 20:53 ` Peter Zijlstra
2019-12-13 10:47 ` Luc Van Oostenryck
2019-12-13 12:56 ` Peter Zijlstra
2019-12-13 14:28 ` Luc Van Oostenryck
2019-12-12 20:49 ` Linus Torvalds
2019-12-13 13:17 ` Arnd Bergmann
2019-12-13 21:32 ` Arnd Bergmann
2019-12-13 22:01 ` Linus Torvalds
2019-12-16 10:28 ` Will Deacon
2019-12-16 11:47 ` Peter Zijlstra
2019-12-16 12:06 ` Arnd Bergmann
2019-12-17 17:07 ` Will Deacon
2019-12-17 18:04 ` Linus Torvalds
2019-12-17 18:05 ` Linus Torvalds
2019-12-17 18:31 ` Will Deacon
2019-12-17 18:32 ` Linus Torvalds
2019-12-18 12:17 ` Michael Ellerman
2019-12-19 12:11 ` Will Deacon
2019-12-18 10:22 ` Christian Borntraeger
2019-12-18 10:35 ` Will Deacon
2019-12-13 12:07 ` Michael Ellerman
2019-12-13 13:53 ` Segher Boessenkool
2019-12-13 21:06 ` Michael Ellerman
2019-12-12 15:10 ` Segher Boessenkool
2019-12-06 22:15 ` [GIT PULL] Please pull powerpc/linux.git powerpc-5.5-2 tag (topic/kasan-bitops) pr-tracker-bot
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