Re: Cast "const char " pointers to "char " to avoid compiler warnings.

Corinna Vinschen <[email protected]> Wed, 10 Oct 2018 17:01:56 +0200
Newsgroups	gmane.comp.lib.newlib
Message-ID	<[email protected]>
On Oct 10 16:37, Christophe Lyon wrote:
> On Wed, 10 Oct 2018 at 11:22, Corinna Vinschen <[email protected]> wrote:
> >
> > On Oct  2 11:10, Christophe Lyon wrote:
> > > On Tue, 2 Oct 2018 at 00:50, Craig Howland <[email protected]> wrote:
> > > >
> > > > On 10/01/2018 05:33 PM, Christophe Lyon wrote:
> > > > > Hi,
> > > > >
> > > > > GCC complains that some assignments loose the const-ness of several
> > > > > data. This small patch adds explicit (char *) casts, but I'm not
> > > > > familiar enough with what newlib does with these to be sure that they
> > > > > are not modified. Maybe the proper fix would be to declare the
> > > > > destinations as "const"?
> > > > >
> > > > > Christophe
> > > > If I understand what you're saying properly, it amounts to saying that you did
> > > > not verify whether the GCC warnings about discarding const are valid or not, yet
> > > > you are suppressing them.  Is this a proper understanding?  If so, it seems like
> > > > these proposed patches are a bad idea, as they might be hiding a real problem,
> > > > or changing the wrong thing.  (In a very quick look at locale.c, for example,
> > > > locale can definitely be written to--it is definitely not const. This implies
> > > > that the const on new_locale is what is wrong.)
> > >
> > > I did have this "very quick look at locale.c" before writing the
> > > patch, and not adding
> > > the cast at the assignment point means removing "const" from __loadlocale()
> > > prototype:
> > > char *__loadlocale (struct __locale_t *loc, int category, const char
> > > *new_locale)
> > > which in turn has a significant impact on the callers which I hope
> > > people familiar
> > > with this area can confirm, or not.
> >
> > The bug was, in fact, to define the third parameter as const, given it
> > gets potentially overwritten.  None of the incoming values is const
> > anyway.  I pushed a patch.
> >
> 
> Thanks.
> 
> However, when building for aarch64, I'm still seeing:
> newlib/libc/ctype/ctype_.c:179:16: warning: assignment discards
> ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
> 
> And I think my patch (or something similar) is still needed for jp2uc.c ?

I only had a look into the __loadlocal issue due to this discussion.
For everything else, please send a new patch.


Corinna

-- 
Corinna Vinschen
Cygwin Maintainer
Red Hat
signature.asc (application/pgp-signature, 833 B)