[PATCH] avoid GCC 10 warning -Wstringop-truncation

[Gedare Bloom]

On Thu, Jul 30, 2020 at 11:52 AM Sebastian Huber
<sebastian.huber at embedded-brains.de> wrote:
>
> On 30/07/2020 18:05, Gedare Bloom wrote:
>
> > On Thu, Jul 30, 2020 at 9:55 AM Sebastian Huber
> > <sebastian.huber at embedded-brains.de> wrote:
> >> On 30/07/2020 17:53, Gedare Bloom wrote:
> >>
> >>> On Thu, Jul 30, 2020 at 9:44 AM Sebastian Huber
> >>> <sebastian.huber at embedded-brains.de>  wrote:
> >>>> On 30/07/2020 13:36, Aschref Ben-Thabet wrote:
> >>>>
> >>>>> diff --git a/testsuites/psxtests/psxndbm01/init.c b/testsuites/psxtests/psxndbm01/init.c
> >>>>> index a13afa7315..b524aff0df 100644
> >>>>> --- a/testsuites/psxtests/psxndbm01/init.c
> >>>>> +++ b/testsuites/psxtests/psxndbm01/init.c
> >>>>> @@ -218,7 +218,7 @@ rtems_task Init(rtems_task_argument ignored)
> >>>>>
> >>>>>       puts( "Fetch non-existing record and confirm error." );
> >>>>>       test_strings = (char*)malloc(6);
> >>>>> -  strncpy( test_strings, "Hello", 5 );
> >>>>> +  memcpy( test_strings, "Hello", 5 );
> >>>>>
> >>>>>       test_strings[5] = '\0';
> >>>> In the glibc devel list this approach was suggested for problems like this:
> >>>>
> >>>> *(char *) mempcpy( test_strings, "Hello", 5 ) = '\0';
> >>>>
> >>>> https://sourceware.org/legacy-ml/libc-alpha/2000-08/msg00061.html
> >>>>
> >>> This code is suspect/wrong. that should create a NUL at the start of
> >>> the test_strings. I'd rather see the memcpy followed by appending the
> >>> NUL. It is easy enough to understand I think.
> >> Yes, this was also my impression then I did read this code snippet.
> >> Please note that this is memPcpy(), a GNU extension.
> > thanks, I had missed that.
> >
> > I don't think there is an easy generalized way to do the delimiting
> > with the standard memcpy. You could do it in one line, if we really
> > wanted something like:
> >
> > ((char *) memcpy (test_strings, "Hello", 5 ))[5] = '\0';
> >
> > We could even create a little helper to do it if it is a common pattern.
>
> The mempcpy() is also available in Newlib.
>
> The only thing I know is that strncpy() is a useless function. With the
> new GCC warnings it is nearly impossible to use correctly. This function
> is an historic accident.
>
> There are several ways to fix the warnings and I think there is no clear
> direction. We basically have the option to use the OpenBSD invented
> strlcpy() and strlcat() functions or some sort of memcpy() and
> mempcpy(). I think the OpenBSD philosophy is that if you put something
> in the strl*() and then at least a C-string is created. This may help to
> contain software bugs a bit and hinder error propagation. The glibc
> developer philosophy is probably that they only care about correct code
> and if you make mistakes that you can go to hell.
>

I'd prefer strl* when it is specifically two strings being manipulated
so that we can leverage the (limited) type checking. The mempcpy could
be used when assembling several strings to optimize slightly.