From: Peter Zijlstra <peterz@infradead.org>
To: Will Deacon <will@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.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 21:53:38 +0100 [thread overview]
Message-ID: <20191212205338.GB11802@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20191212202157.GD11457@worktop.programming.kicks-ass.net>
On Thu, Dec 12, 2019 at 09:21:57PM +0100, Peter Zijlstra wrote:
> On Thu, Dec 12, 2019 at 07:34:01PM +0000, Will Deacon wrote:
> > void ool_store_release(volatile unsigned long *ptr, unsigned long val)
> > {
> > smp_store_release(ptr, val);
> > }
> >
> > 0000000000000000 <ool_store_release>:
> > 0: a9be7bfd stp x29, x30, [sp, #-32]!
> > 4: 90000002 adrp x2, 0 <__stack_chk_guard>
> > 8: 91000042 add x2, x2, #0x0
> > c: 910003fd mov x29, sp
> > 10: f9400043 ldr x3, [x2]
> > 14: f9000fa3 str x3, [x29, #24]
> > 18: d2800003 mov x3, #0x0 // #0
> > 1c: c89ffc01 stlr x1, [x0]
> > 20: f9400fa1 ldr x1, [x29, #24]
> > 24: f9400040 ldr x0, [x2]
> > 28: ca000020 eor x0, x1, x0
> > 2c: b5000060 cbnz x0, 38 <ool_store_release+0x38>
> > 30: a8c27bfd ldp x29, x30, [sp], #32
> > 34: d65f03c0 ret
> > 38: 94000000 bl 0 <__stack_chk_fail>
> >
> > It's a mess, and fixing READ_ONCE() doesn't help this case, which is why
> > I was looking at getting rid of volatile where it's not strictly needed.
> > I'm certainly open to other suggestions, I just haven't managed to think
> > of anything else.
>
> We could move the kernel to C++ and write:
>
> std::remove_volatile<typeof(p)>::type __p = (p);
>
> /me runs like hell...
Also, the GCC __auto_type thing strips _Atomic and const qualifiers but
for some obscure raisin forgets to strip volatile :/
https://gcc.gnu.org/ml/gcc-patches/2013-11/msg01378.html
Now, looking at the current GCC source:
https://github.com/gcc-mirror/gcc/blob/97d7270f894395e513667a031a0c309d1819d05e/gcc/c/c-parser.c#L3707
it seems that __typeof__() is supposed to strip all qualifiers from
_Atomic types. That lead me to try:
typeof(_Atomic typeof(p)) __p = (p);
But alas, I still get the same junk you got for ool_store_release() :/
next prev parent reply other threads:[~2019-12-12 20:54 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
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 [this message]
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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