RFR(XS): 8214707: Prevent GCC 8 from reporting error in ClassLoader::file_name_for_class_name()

[Thomas Stüfe]

On Fri, Dec 7, 2018 at 2:09 AM David Holmes <david.holmes at oracle.com> wrote:
>
> +1
>
> Annoying to have to workaround a buggy compiler though. :(
>

I do not think this is a compiler bug but a usage error which in this
case was harmless.

I think the compiler warning is correct.

strncpy(dest, src, destlen)

destlen should be the size of the receiving buffer. It should not be
the string len of the source string. This seems to be a common
misunderstanding, I keep seeing this.

In this case, super-correct would be something like this:

size_t remaining = <buffer len>
strncpy(file_name, class_name, remaining);
size_t written = strlen(file_name)
remaining -= written
strncpy(file_name + written, class_suffix, remaining);

strncpy has other problems though, not zero-terminating on truncation,
and weirdly enough \0 padding destination to its end (none of which
apply here).

I usually rather use snprintf, e.g.:

jio_snprintf(file_name, bufferlen, "%s%s", class_name, class_suffix);

it is shorter and one needs not to know the size of the components and
it takes care of truncation correctly and does not waste time to pad
the destination.

Just my 5c...

Cheers, Thomas




> Thanks,
> David
>
> On 7/12/2018 6:44 am, Harold David Seigel wrote:
> > Hi Dmitry,
> >
> > Could you change the type of class_suffix_len from int to size_t ?
> > Otherwise, it looks good.  (I don't need to see a new webrev.)
> >
> > Thanks, Harold
> >
> >
> > On 12/6/2018 3:19 PM, Dmitry Chuyko wrote:
> >> Hello,
> >>
> >> Please review a small fix for an error reported by GCC 8. It's a false
> >> positive and minor code clean-up silences the compiler: suffix length
> >> is extracted into a variable.
> >>
> >> bug: https://bugs.openjdk.java.net/browse/JDK-8214707
> >> webrev: http://cr.openjdk.java.net/~dchuyko/8214707/webrev.00/
> >> testing: submit repo
> >> (mach5-one-dchuyko-JDK-8214707-20181206-1906-13407: PASSED)
> >>
> >> -Dmitry
> >>
> >