svn commit: r333860 - head/sys/kern

[Matthew Macy]

On Wed, May 23, 2018 at 11:42 PM, Michael Tuexen
<Michael.Tuexen at macmic.franken.de> wrote:
>> On 24. May 2018, at 08:36, Matthew Macy <mmacy at freebsd.org> wrote:
>>
>> On Wed, May 23, 2018 at 11:35 PM, Michael Tuexen
>> <Michael.Tuexen at macmic.franken.de> wrote:
>>>> On 24. May 2018, at 06:51, Matthew Macy <mmacy at freebsd.org> 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 <glebius at 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 at 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> ==============================================================================
>>>>> 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
>>>>
>>>
>