Date: Thu, 24 May 2018 08:42:18 +0200 From: Michael Tuexen <Michael.Tuexen@macmic.franken.de> To: Matthew Macy <mmacy@freebsd.org> Cc: Gleb Smirnoff <glebius@freebsd.org>, src-committers <src-committers@freebsd.org>, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r333860 - head/sys/kern Message-ID: <ABB8E26D-ABAE-42E6-9A1C-FAD0E8DDA3C6@macmic.franken.de> In-Reply-To: <CAPrugNooA9Jfx5=h8fYb5%2BKPUOjSOD_NR8QX=bBkVKCAu=96-A@mail.gmail.com> References: <201805190510.w4J5AqfS054367@repo.freebsd.org> <20180523222743.GU71675@FreeBSD.org> <CAPrugNpKxEVx%2Bg0D6qUwq=yw_W-QeuntupwAjteK1yALkJktag@mail.gmail.com> <20180523225729.GV71675@FreeBSD.org> <CAPrugNpsiYQ1MKkgGbkwPEeTcsTCdD_u5GAvYpMJKHzeSbCL=w@mail.gmail.com> <20180524044252.GW71675@FreeBSD.org> <CAPrugNoVPCbB0qTY=Z1dwCZ%2BbCbVbA1d5b0-tw5qaPxWRK0q8g@mail.gmail.com> <5B9EE208-384F-44AD-9B47-059D77FE9B34@macmic.franken.de> <CAPrugNooA9Jfx5=h8fYb5%2BKPUOjSOD_NR8QX=bBkVKCAu=96-A@mail.gmail.com>
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> On 24. May 2018, at 08:36, Matthew Macy <mmacy@freebsd.org> wrote: >=20 > On Wed, May 23, 2018 at 11:35 PM, Michael Tuexen > <Michael.Tuexen@macmic.franken.de> wrote: >>> On 24. May 2018, at 06:51, Matthew Macy <mmacy@freebsd.org> wrote: >>>=20 >>> 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... >=20 > 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... Best regards Michael > -M >=20 >=20 >>=20 >> Best regards >> Michael >>> quite a number of real issues from compiling with gcc8. >>>=20 >>> If you want to _actually_ be helpful fix these: >>> https://people.freebsd.org/~mmacy/gcc8logs/GENERIC-NODEBUG.log >>>=20 >>> https://people.freebsd.org/~mmacy/gcc8logs/GENERIC.log >>>=20 >>> On Wed, May 23, 2018 at 9:42 PM, Gleb Smirnoff <glebius@freebsd.org> = wrote: >>>> Let me repeat again. The warning is a false positive, and thus = assignment >>>> isn't useful. I'm not worried about a single instruction, more = about >>>> polluting the code. >>>>=20 >>>> If the warning was escalated to build error, and we did carry about >>>> building with gcc8, in this case the assignment should be added = with >>>> a comment /* pacify gcc */. >>>>=20 >>>> 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 = <glebius@freebsd.org> 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 = <glebius@freebsd.org> 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> = =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D >>>> 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 =3D 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 =3D=3D 0) { >>>> M> > M> > M> sfio =3D NULL; >>>> M> > M> > M> nios =3D 0; >>>> M> > M> > M> + npages =3D 0; >>>> M> > M> > M> goto prepend_header; >>>> M> > M> > M> } >>>> M> > M> > M> hdr_uio =3D 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 =3D=3D 0, we = won't ever use npages. >>>> M> > M> > >>>> M> > M> > -- >>>> M> > M> > Gleb Smirnoff >>>> M> > >>>> M> > -- >>>> M> > Gleb Smirnoff >>>>=20 >>>> -- >>>> Gleb Smirnoff >>>=20 >>=20
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