From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755175AbeEHNB4 (ORCPT ); Tue, 8 May 2018 09:01:56 -0400 Received: from mail.kmu-office.ch ([178.209.48.109]:42270 "EHLO mail.kmu-office.ch" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754776AbeEHNBy (ORCPT ); Tue, 8 May 2018 09:01:54 -0400 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Date: Tue, 08 May 2018 15:01:53 +0200 From: Stefan Agner To: Robin Murphy Cc: arm@kernel.org, arnd@arndb.de, linux@armlinux.org.uk, ard.biesheuvel@linaro.org, nicolas.pitre@linaro.org, marc.zyngier@arm.com, behanw@converseincode.com, keescook@chromium.org, Bernhard.Rosenkranzer@linaro.org, mka@chromium.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [RESEND PATCH v2] bus: arm-cci: use asm unreachable In-Reply-To: <9925be9a-2e24-7ab4-4d7e-cb8f62c422e7@arm.com> References: <20180508113211.7026-1-stefan@agner.ch> <9925be9a-2e24-7ab4-4d7e-cb8f62c422e7@arm.com> Message-ID: User-Agent: Roundcube Webmail/1.3.4 X-Spamd-Result: default: False [-3.10 / 15.00]; MID_RHS_MATCH_FROM(0.00)[]; ASN(0.00)[asn:29691, ipnet:2a02:418::/29, country:CH]; ARC_NA(0.00)[]; MIME_GOOD(-0.10)[text/plain]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCPT_COUNT_TWELVE(0.00)[13]; DKIM_SIGNED(0.00)[]; BAYES_HAM(-3.00)[99.98%]; RCVD_COUNT_ZERO(0.00)[0]; FROM_EQ_ENVFROM(0.00)[]; TO_DN_SOME(0.00)[]; FROM_HAS_DN(0.00)[]; RCVD_TLS_ALL(0.00)[] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08.05.2018 14:19, Robin Murphy wrote: > On 08/05/18 12:32, Stefan Agner wrote: >> Mixing asm and C code is not recommended in a naked function by >> gcc and leads to an error when using clang: >> drivers/bus/arm-cci.c:2107:2: error: non-ASM statement in naked >> function is not supported >> unreachable(); >> ^ >> >> While the function is marked __naked it actually properly return >> in asm. There is no need for the unreachable() call. > > The commit title is a bit out-of-date now (I guess it could just be > something like "remove unnecessary unreachable()" now), but the rest > looks OK to me - even GCC clearly doesn't expect anything beyond the > asm to be reachable anyway since the lack of epilogue includes the > lack of any compiler-generated return. I've checked that GCC 7.2 > generates identical object files before and after, other than (for > obvious reasons) the line numbers generated by WANT_WARN_ON_SLOWPATH > for all the WARN()s appearing later in the file. Title: Oops, good catch! Will send a v3. Thanks for checking gcc. -- Stefan > > Reviewed-by: Robin Murphy > >> Suggested-by: Russell King >> Signed-off-by: Stefan Agner >> Acked-by: Nicolas Pitre >> --- >> drivers/bus/arm-cci.c | 2 -- >> 1 file changed, 2 deletions(-) >> >> diff --git a/drivers/bus/arm-cci.c b/drivers/bus/arm-cci.c >> index 443e4c3fd357..b8184a903583 100644 >> --- a/drivers/bus/arm-cci.c >> +++ b/drivers/bus/arm-cci.c >> @@ -371,8 +371,6 @@ asmlinkage void __naked cci_enable_port_for_self(void) >> [sizeof_struct_cpu_port] "i" (sizeof(struct cpu_port)), >> [sizeof_struct_ace_port] "i" (sizeof(struct cci_ace_port)), >> [offsetof_port_phys] "i" (offsetof(struct cci_ace_port, phys)) ); >> - >> - unreachable(); >> } >> /** >> From mboxrd@z Thu Jan 1 00:00:00 1970 From: stefan@agner.ch (Stefan Agner) Date: Tue, 08 May 2018 15:01:53 +0200 Subject: [RESEND PATCH v2] bus: arm-cci: use asm unreachable In-Reply-To: <9925be9a-2e24-7ab4-4d7e-cb8f62c422e7@arm.com> References: <20180508113211.7026-1-stefan@agner.ch> <9925be9a-2e24-7ab4-4d7e-cb8f62c422e7@arm.com> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 08.05.2018 14:19, Robin Murphy wrote: > On 08/05/18 12:32, Stefan Agner wrote: >> Mixing asm and C code is not recommended in a naked function by >> gcc and leads to an error when using clang: >> drivers/bus/arm-cci.c:2107:2: error: non-ASM statement in naked >> function is not supported >> unreachable(); >> ^ >> >> While the function is marked __naked it actually properly return >> in asm. There is no need for the unreachable() call. > > The commit title is a bit out-of-date now (I guess it could just be > something like "remove unnecessary unreachable()" now), but the rest > looks OK to me - even GCC clearly doesn't expect anything beyond the > asm to be reachable anyway since the lack of epilogue includes the > lack of any compiler-generated return. I've checked that GCC 7.2 > generates identical object files before and after, other than (for > obvious reasons) the line numbers generated by WANT_WARN_ON_SLOWPATH > for all the WARN()s appearing later in the file. Title: Oops, good catch! Will send a v3. Thanks for checking gcc. -- Stefan > > Reviewed-by: Robin Murphy > >> Suggested-by: Russell King >> Signed-off-by: Stefan Agner >> Acked-by: Nicolas Pitre >> --- >> drivers/bus/arm-cci.c | 2 -- >> 1 file changed, 2 deletions(-) >> >> diff --git a/drivers/bus/arm-cci.c b/drivers/bus/arm-cci.c >> index 443e4c3fd357..b8184a903583 100644 >> --- a/drivers/bus/arm-cci.c >> +++ b/drivers/bus/arm-cci.c >> @@ -371,8 +371,6 @@ asmlinkage void __naked cci_enable_port_for_self(void) >> [sizeof_struct_cpu_port] "i" (sizeof(struct cpu_port)), >> [sizeof_struct_ace_port] "i" (sizeof(struct cci_ace_port)), >> [offsetof_port_phys] "i" (offsetof(struct cci_ace_port, phys)) ); >> - >> - unreachable(); >> } >> /** >>