Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932613AbdHWTCn (ORCPT ); Wed, 23 Aug 2017 15:02:43 -0400 Received: from mail-oi0-f65.google.com ([209.85.218.65]:36813 "EHLO mail-oi0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932458AbdHWTCl (ORCPT ); Wed, 23 Aug 2017 15:02:41 -0400 MIME-Version: 1.0 In-Reply-To: <20170823150143.2746796-1-arnd@arndb.de> References: <20170823150143.2746796-1-arnd@arndb.de> From: Arnd Bergmann Date: Wed, 23 Aug 2017 21:02:39 +0200 X-Google-Sender-Auth: TWai0LKjcG7liqlIGF2JPxcrU60 Message-ID: Subject: Re: [PATCH] scsi: lpfc: avoid false-positive gcc-8 warning To: James Smart , Dick Kennedy , "James E.J. Bottomley" , "Martin K. Petersen" Cc: Arnd Bergmann , Hannes Reinecke , linux-scsi , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3116 Lines: 65 On Wed, Aug 23, 2017 at 5:01 PM, Arnd Bergmann wrote: > This is an interesting regression with gcc-8, showing a harmless > warning for correct code: > > In file included from include/linux/kernel.h:13:0, > ... > from drivers/scsi/lpfc/lpfc_debugfs.c:23: > include/linux/printk.h:301:2: error: 'eq' may be used uninitialized in this function [-Werror=maybe-uninitialized] > printk(KERN_ERR pr_fmt(fmt), ##__VA_ARGS__) > ^~~~~~ > In file included from drivers/scsi/lpfc/lpfc_debugfs.c:58:0: > drivers/scsi/lpfc/lpfc_debugfs.h:451:31: note: 'eq' was declared here > > I tried to come up with a reduced test case for gcc here > a few times, but every time ended up with code that is actually > wrong with older gcc versions missing the bug and gcc-8 finding > it. As this is the only false-positive -Wmaybe-uninitialized > warnign I got with gcc-8 randconfig builds, I'd suggest we > work around it. > > Making the index variable 'unsigned' is enough to shut up > the warning, as gcc can then see that comparing eqidx to > phba->io_channel_irqs is fine here. > > Signed-off-by: Arnd Bergmann Sorry, I have to retract my patch. While it apparently solved the problem for most randconfig builds, I have now run into another case that it did not address, and I still get the warning for one caller: In file included from /git/arm-soc/include/linux/kernel.h:13:0, from /git/arm-soc/arch/x86/include/asm/percpu.h:44, from /git/arm-soc/arch/x86/include/asm/current.h:5, from /git/arm-soc/include/linux/sched.h:11, from /git/arm-soc/include/linux/blkdev.h:4, from /git/arm-soc/drivers/scsi/lpfc/lpfc_debugfs.c:23: /git/arm-soc/drivers/scsi/lpfc/lpfc_debugfs.c: In function 'lpfc_debug_dump_all_queues': /git/arm-soc/include/linux/printk.h:301:2: error: 'eq' may be used uninitialized in this function [-Werror=maybe-uninitialized] printk(KERN_ERR pr_fmt(fmt), ##__VA_ARGS__) ^~~~~~ In file included from /git/arm-soc/drivers/scsi/lpfc/lpfc_debugfs.c:58:0: /git/arm-soc/drivers/scsi/lpfc/lpfc_debugfs.h:451:31: note: 'eq' was declared here struct lpfc_queue *wq, *cq, *eq; ^~ In file included from /git/arm-soc/include/linux/kernel.h:13:0, from /git/arm-soc/arch/x86/include/asm/percpu.h:44, from /git/arm-soc/arch/x86/include/asm/current.h:5, from /git/arm-soc/include/linux/sched.h:11, from /git/arm-soc/include/linux/blkdev.h:4, from /git/arm-soc/drivers/scsi/lpfc/lpfc_debugfs.c:23: /git/arm-soc/include/linux/printk.h:301:2: error: 'eq' may be used uninitialized in this function [-Werror=maybe-uninitialized] printk(KERN_ERR pr_fmt(fmt), ##__VA_ARGS__) ^~~~~~ In file included from /git/arm-soc/drivers/scsi/lpfc/lpfc_debugfs.c:58:0: /git/arm-soc/drivers/scsi/lpfc/lpfc_debugfs.h:451:31: note: 'eq' was declared here struct lpfc_queue *wq, *cq, *eq; ^~ cc1: all warnings being treated as errors Arnd