svn commit: r333860 - head/sys/kern

[Michael Tuexen]

> 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...

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
>