From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753065AbdIFVdF (ORCPT ); Wed, 6 Sep 2017 17:33:05 -0400 Received: from mx1.redhat.com ([209.132.183.28]:57728 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752306AbdIFVdD (ORCPT ); Wed, 6 Sep 2017 17:33:03 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 9EC3CC047B69 Authentication-Results: ext-mx07.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx07.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=jpoimboe@redhat.com Date: Wed, 6 Sep 2017 16:33:02 -0500 From: Josh Poimboeuf To: Miguel Bernal Marin Cc: Peter Zijlstra , Ingo Molnar , Thomas Gleixner , "H . Peter Anvin" , linux-kernel@vger.kernel.org, x86@kernel.org Subject: Re: [PATCH 3/3] locking/rwsem/x86: Add stack frame dependency for __downgrade_write() Message-ID: <20170906213302.s6st6ch32hixhwmg@treble> References: <20170906052613.30058-1-miguel.bernal.marin@linux.intel.com> <20170906052613.30058-4-miguel.bernal.marin@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20170906052613.30058-4-miguel.bernal.marin@linux.intel.com> User-Agent: Mutt/1.6.0.1 (2016-04-01) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.31]); Wed, 06 Sep 2017 21:33:03 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 06, 2017 at 12:26:13AM -0500, Miguel Bernal Marin wrote: > kernel/locking/rwsem.o: warning: objtool: downgrade_write()+0x22: call without frame pointer save/setup > > The warning means gcc 7.2.0 placed the __downgrade_write() inline asm (and > its call instruction) before the frame pointer setup in downgrade_write(), > which breaks frame pointer convention and can result in incorrect > stack traces. > > Force a stack frame to be created before the call instruction by listing > the stack pointer as an output operand in the inline asm statement. > > Signed-off-by: Miguel Bernal Marin > --- > arch/x86/include/asm/rwsem.h | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/include/asm/rwsem.h b/arch/x86/include/asm/rwsem.h > index d26b6916b935..a749dc6a3103 100644 > --- a/arch/x86/include/asm/rwsem.h > +++ b/arch/x86/include/asm/rwsem.h > @@ -205,8 +205,10 @@ static inline void __up_write(struct rw_semaphore *sem) > */ > static inline void __downgrade_write(struct rw_semaphore *sem) > { > + register void *__sp asm(_ASM_SP); > + > asm volatile("# beginning __downgrade_write\n\t" > - LOCK_PREFIX _ASM_ADD "%2,(%1)\n\t" > + LOCK_PREFIX _ASM_ADD "%2,(%2)\n\t" The '%2' should be changed to '%3' LOCK_PREFIX _ASM_ADD "%3,(%2)\n\t" because both inputs' indices are shifted by the new output constraint. > /* > * transitions 0xZZZZ0001 -> 0xYYYY0001 (i386) > * 0xZZZZZZZZ00000001 -> 0xYYYYYYYY00000001 (x86_64) > @@ -215,7 +217,7 @@ static inline void __downgrade_write(struct rw_semaphore *sem) > " call call_rwsem_downgrade_wake\n" > "1:\n\t" > "# ending __downgrade_write\n" > - : "+m" (sem->count) > + : "+m" (sem->count), "+r" (__sp) > : "a" (sem), "er" (-RWSEM_WAITING_BIAS) > : "memory", "cc"); -- Josh