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

[Kim Barrett]

> On Sep 1, 2020, at 4:57 AM, Thomas Schatzl <thomas.schatzl at oracle.com> wrote:
> 
> Hi,
> 
> On 01.09.20 10:48, serguei.spitsyn at oracle.com wrote:
>> Hi Eric,
>> It looks good to me.
>> Thank you for taking care about it.
>> Thanks,
>> Serguei
>> On 9/1/20 01:15, Eric Liu 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
>>> 
> 
> Looks good.
> 
> Maybe the comment in compileBroker.hpp could be improved by specifying a gcc version and/or gcc bug number (not sure if done elsewhere too) - so that it can be verified/removed at some point.
> 
> 66       // This code can incorrectly cause a "stringop-truncation" warning with gcc

We don’t really know what gcc versions are relevant, and there’s a whole pile of
gcc bugs for -Wstringop-truncation (currently 22 open bugs).  Figuring out which
one or ones it is doesn’t seem like a good use of time.

> 
> Or, alternatively by specifying a type in the enum (we are on c++14 now...), the cast to size_t and could go away and with it the error? (If it is the cause of the gcc error).

Or don’t use an enum, but change it to an appropriately typed static constant.
I don’t know if the cast has anything to do with -Wstringop-truncation being confused, but
as I had the same thought, that seems worth a try.