PING 2 [PATCH] refine -Wstringop-truncation and -Wsizeof-pointer-memaccess for strncat of nonstrings (PR 85602)

[Martin Sebor <msebor at gmail dot com>]

Ping: https://gcc.gnu.org/ml/gcc-patches/2018-05/msg01671.html

(In IRC last week Franz reported successfully testing the patch.
Thanks again.)

On 05/29/2018 01:21 PM, Martin Sebor wrote:
> To make review and testing easier (thank you, Franz), attached
> is an updated patch rebased on top of today's trunk.
>
> (Note that the patch intentionally doesn't suppress the warning
> for the submitted test case without adding the nonstring attribute.)
>
> On 05/25/2018 02:59 PM, Martin Sebor wrote:
> > Ping:
> > https://gcc.gnu.org/ml/gcc-patches/2018-05/msg00869.html
> >
> > On 05/17/2018 08:01 PM, Martin Sebor wrote:
> > > The -Wstringop-truncation and -Wsizeof-pointer-memaccess warnings
> > > I added and enhanced, respectively, in GCC 8 are arguably overly
> > > strict for source arguments declared with the nonstring attribute.
> > >
> > > For example, -Wsizeof-pointer-memaccess triggers for the strncat
> > > call below:
> > >
> > >   __attribute__ ((nonstring)) char nonstr[8];
> > >   extern char *d;
> > >   strncat (d, nonstr, sizeof nonstr);
> > >
> > > even though it's still a fairly common (if unsafe) idiom from
> > > the early UNIX days (V7 from 1979 to be exact) where strncat
> > > was introduced.  (This use case, modulo the attribute, was
> > > reduced from coreutils.)
> > >
> > > Simialrly, -Wstringop-truncation warns for some strcat calls that
> > > are actually safe, such as in:
> > >
> > >   strcpy (nonstr, "123");
> > >   strncat (d, nonstr, 32);
> > >
> > > To help with the adoption of the warnings and the attribute and
> > > avoid unnecessary churn the attached patch relaxes both warnings
> > > to accept code like this without diagnostics.
> > >
> > > The patch doesn't add any new warnings so I'd like it considered
> > > for GCC 8 in addition to trunk.
> > >
> > > Thanks
> > > Martin