RFR(S): 8252407: Build failure with gcc-8+ and asan

[Kim Barrett]

> On Sep 1, 2020, at 4:01 AM, Eric Liu <eric.c.liu at arm.com> wrote:
> 
> Hi all,
> 
> Please review this simple change to fix some compile warnings.
> 
> The newer gcc (gcc-8 or higher) would warn for calls to bounded string
> manipulation functions such as 'strncpy' that may either truncate the
> copied string or leave the destination unchanged.
> 
> This patch fixed stringop-truncation warnings reported by gcc, some of
> them only appear when compiled with "--enable-asan".
> 
> [TESTS]
> Jtreg: hotspot::hotspot_all_no_apps, jdk::jdk_core and langtools::tier1.
> No new failure found.
> 
> http://cr.openjdk.java.net/~qfeng/ericliu/jdk/stringop_trunc/webrev.00/
> https://bugs.openjdk.java.net/browse/JDK-8252407
> 
> Thanks,
> Eric

I really hate -Wstringop-truncation.  It's been a constant source of churn
for us ever since it appeared.  The changes being made to getIndex and
getFlags (NetworkInterface.c) are modifying lines that were changed very
recently to deal with such warnings from gcc10.  I'm worried that these new
changes will re-trigger warnings from gcc10 (though this change isn't a
revert; the gcc10 warning was justifiable).  I think it should be okay, but
there’s some risk here.

Changes look good, subject to that caveat.  I think these changes conform
better to the documented description of the warning than did the recent
NetworkInterface.c change mentioned above, so I’m hopeful that we’re not
in a warning cycle here.  But it would be good to have someone test these
changes against gcc10.x.