svn commit: r333860 - head/sys/kern

[Michael Tuexen]

> 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...

Best regards
Michael
> -M
> 
> 
>> 
>> Best regards
>> Michael
>>> quite a number of real issues from compiling with gcc8.
>>> 
>>> If you want to _actually_ be helpful fix these:
>>> https://people.freebsd.org/~mmacy/gcc8logs/GENERIC-NODEBUG.log
>>> 
>>> https://people.freebsd.org/~mmacy/gcc8logs/GENERIC.log
>>> 
>>> On Wed, May 23, 2018 at 9:42 PM, Gleb Smirnoff <glebius at 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.
>>>> 
>>>> 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 */.
>>>> 
>>>> 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
>>> 
>>