From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra 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 Message-ID: <20191212205338.GB11802@worktop.programming.kicks-ass.net> References: <20191206131650.GM2827@hirez.programming.kicks-ass.net> <875zimp0ay.fsf@mpe.ellerman.id.au> <20191212080105.GV2844@hirez.programming.kicks-ass.net> <20191212100756.GA11317@willie-the-truck> <20191212104610.GW2827@hirez.programming.kicks-ass.net> <20191212180634.GA19020@willie-the-truck> <20191212193401.GB19020@willie-the-truck> <20191212202157.GD11457@worktop.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20191212202157.GD11457@worktop.programming.kicks-ass.net> Sender: linux-kernel-owner@vger.kernel.org To: Will Deacon Cc: Linus Torvalds , Michael Ellerman , dja@axtens.net, Linux Kernel Mailing List , linuxppc-dev@lists.ozlabs.org, Christophe Leroy , linux-arch , Mark Rutland , Segher Boessenkool , Arnd Bergmann , Christian Borntraeger List-Id: linux-arch.vger.kernel.org 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 : > > 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 > > 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::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() :/ From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from merlin.infradead.org ([205.233.59.134]:43398 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730864AbfLLUyO (ORCPT ); Thu, 12 Dec 2019 15:54:14 -0500 Date: Thu, 12 Dec 2019 21:53:38 +0100 From: Peter Zijlstra Subject: Re: READ_ONCE() + STACKPROTECTOR_STRONG == :/ (was Re: [GIT PULL] Please pull powerpc/linux.git powerpc-5.5-2 tag (topic/kasan-bitops)) Message-ID: <20191212205338.GB11802@worktop.programming.kicks-ass.net> References: <20191206131650.GM2827@hirez.programming.kicks-ass.net> <875zimp0ay.fsf@mpe.ellerman.id.au> <20191212080105.GV2844@hirez.programming.kicks-ass.net> <20191212100756.GA11317@willie-the-truck> <20191212104610.GW2827@hirez.programming.kicks-ass.net> <20191212180634.GA19020@willie-the-truck> <20191212193401.GB19020@willie-the-truck> <20191212202157.GD11457@worktop.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191212202157.GD11457@worktop.programming.kicks-ass.net> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Will Deacon Cc: Linus Torvalds , Michael Ellerman , dja@axtens.net, Linux Kernel Mailing List , linuxppc-dev@lists.ozlabs.org, Christophe Leroy , linux-arch , Mark Rutland , Segher Boessenkool , Arnd Bergmann , Christian Borntraeger Message-ID: <20191212205338.bgSdqNnNj50-QDVYITwNfi08bOkMbPDurSVWKCi-TdE@z> 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 : > > 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 > > 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::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() :/