From owner-svn-src-head@freebsd.org Thu May 24 06:53:44 2018 Return-Path: Delivered-To: svn-src-head@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 50E90F5D631; Thu, 24 May 2018 06:53:44 +0000 (UTC) (envelope-from mmacy@freebsd.org) Received: from smtp.freebsd.org (unknown [IPv6:2610:1c1:1:606c::24b:4]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "smtp.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id F1FD779EDB; Thu, 24 May 2018 06:53:43 +0000 (UTC) (envelope-from mmacy@freebsd.org) Received: from mail-io0-f172.google.com (mail-io0-f172.google.com [209.85.223.172]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) (Authenticated sender: mmacy) by smtp.freebsd.org (Postfix) with ESMTPSA id B7823E9D7; Thu, 24 May 2018 06:53:43 +0000 (UTC) (envelope-from mmacy@freebsd.org) Received: by mail-io0-f172.google.com with SMTP id d11-v6so1017337iof.11; Wed, 23 May 2018 23:53:43 -0700 (PDT) X-Gm-Message-State: ALKqPwcuslqtWsSk0hn3BbmuuJr5uIvv4uHxOgq7kaPUvdrWsQwXgewa H5ylUN9VFYb9SJPw05FqysR4v4EwDq3+wzLSIwI= X-Google-Smtp-Source: ADUXVKLvegGA8Pci8zbyxBrSY4ZDeaCm+zVjEOhhYaaKVhcJsd+WWMidQwXF2pdPPj8IsDhK8q6FyBYHGjzyDNTGghs= X-Received: by 2002:a6b:6707:: with SMTP id b7-v6mr225781ioc.132.1527144823164; Wed, 23 May 2018 23:53:43 -0700 (PDT) MIME-Version: 1.0 Received: by 2002:a02:85ca:0:0:0:0:0 with HTTP; Wed, 23 May 2018 23:53:42 -0700 (PDT) In-Reply-To: References: <201805190510.w4J5AqfS054367@repo.freebsd.org> <20180523222743.GU71675@FreeBSD.org> <20180523225729.GV71675@FreeBSD.org> <20180524044252.GW71675@FreeBSD.org> <5B9EE208-384F-44AD-9B47-059D77FE9B34@macmic.franken.de> From: Matthew Macy Date: Wed, 23 May 2018 23:53:42 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: svn commit: r333860 - head/sys/kern To: Michael Tuexen Cc: Gleb Smirnoff , src-committers , svn-src-all@freebsd.org, svn-src-head@freebsd.org Content-Type: text/plain; charset="UTF-8" X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.26 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 24 May 2018 06:53:44 -0000 On Wed, May 23, 2018 at 11:42 PM, Michael Tuexen wrote: >> On 24. May 2018, at 08:36, Matthew Macy wrote: >> >> On Wed, May 23, 2018 at 11:35 PM, Michael Tuexen >> wrote: >>>> On 24. May 2018, at 06:51, Matthew Macy wrote: >>>> >>>> Warnings find bugs PERIOD. Although most are not useful, I've found >>> Some warnings indicate bugs, some warnings are just wrong. If you >>> have a "may be used uninitialized" warning being a false positive, you >>> may silences the warning by just set it to zero in the declaration and >>> you silence it. Other compilers might then correctly report an >>> assignment without affect... >> >> I have yet to see a double assignment be flagged as assignment without >> effect. If it _does_ occur then we have to disable the warning on the >> compiler that we have less faith in. > Have seen it in the past in a difference project... But you miss my point: > > Not all warnings indicate bugs PERIOD. Some warning are just wrong... Have you read my follow up? _Many_ Many warnings are wrong. Please respond to that on what the global policy should be. The value of any one particular instance of a warning does not merit discussion. -M , in this case the assignment should be added with >>>>> a comment /* pacify gcc */. >>>>> >>>>> On Wed, May 23, 2018 at 03:59:33PM -0700, Matthew Macy wrote: >>>>> M> On Wed, May 23, 2018 at 3:57 PM, Gleb Smirnoff wrote: >>>>> M> > The initialization isn't useful. >>>>> M> >>>>> M> It silences a gcc warning. So yes it is. It's this exchange which is not useful. >>>>> M> >>>>> M> -M >>>>> M> >>>>> M> >>>>> M> > On Wed, May 23, 2018 at 03:52:42PM -0700, Matthew Macy wrote: >>>>> M> > M> Talk to the gcc devs. The warning is useful even if there are false positives. >>>>> M> > M> >>>>> M> > M> On Wed, May 23, 2018 at 3:27 PM, Gleb Smirnoff wrote: >>>>> M> > M> > Hi, >>>>> M> > M> > >>>>> M> > M> > On Sat, May 19, 2018 at 05:10:52AM +0000, Matt Macy wrote: >>>>> M> > M> > M> Author: mmacy >>>>> M> > M> > M> Date: Sat May 19 05:10:51 2018 >>>>> M> > M> > M> New Revision: 333860 >>>>> M> > M> > M> URL: https://svnweb.freebsd.org/changeset/base/333860 >>>>> M> > M> > M> >>>>> M> > M> > M> Log: >>>>> M> > M> > M> sendfile: annotate unused value and ensure that npages is actually initialized >>>>> M> > M> > M> >>>>> M> > M> > M> Modified: >>>>> M> > M> > M> head/sys/kern/kern_sendfile.c >>>>> M> > M> > M> >>>>> M> > M> > M> Modified: head/sys/kern/kern_sendfile.c >>>>> M> > M> > M> ============================================================================== >>>>> M> > M> > M> --- head/sys/kern/kern_sendfile.c Sat May 19 05:09:10 2018 (r333859) >>>>> M> > M> > M> +++ head/sys/kern/kern_sendfile.c Sat May 19 05:10:51 2018 (r333860) >>>>> M> > M> > M> @@ -341,7 +341,7 @@ sendfile_swapin(vm_object_t obj, struct sf_io *sfio, o >>>>> M> > M> > M> } >>>>> M> > M> > M> >>>>> M> > M> > M> for (int i = 0; i < npages;) { >>>>> M> > M> > M> - int j, a, count, rv; >>>>> M> > M> > M> + int j, a, count, rv __unused; >>>>> M> > M> > M> >>>>> M> > M> > M> /* Skip valid pages. */ >>>>> M> > M> > M> if (vm_page_is_valid(pa[i], vmoff(i, off) & PAGE_MASK, >>>>> M> > M> > M> @@ -688,6 +688,7 @@ retry_space: >>>>> M> > M> > M> if (space == 0) { >>>>> M> > M> > M> sfio = NULL; >>>>> M> > M> > M> nios = 0; >>>>> M> > M> > M> + npages = 0; >>>>> M> > M> > M> goto prepend_header; >>>>> M> > M> > M> } >>>>> M> > M> > M> hdr_uio = NULL; >>>>> M> > M> > >>>>> M> > M> > This initialization is redundant and a compiler warning if exists is wrong. >>>>> M> > M> > >>>>> M> > M> > If we jump down to prepend_header with nios == 0, we won't ever use npages. >>>>> M> > M> > >>>>> M> > M> > -- >>>>> M> > M> > Gleb Smirnoff >>>>> M> > >>>>> M> > -- >>>>> M> > Gleb Smirnoff >>>>> >>>>> -- >>>>> Gleb Smirnoff >>>> >>> >