Avoid some GCC 10.X warnings in HotSpot

[Kim Barrett]

> On Jul 8, 2020, at 2:42 PM, Ioi Lam <ioi.lam at oracle.com> wrote:
> 
> 
> 
> On 7/8/20 11:32 AM, Ioi Lam wrote:
>> 
>> 
>> On 7/8/20 11:04 AM, Kim Barrett wrote:
>>>> On Jul 8, 2020, at 8:35 AM, Koichi Sakata <sakatakui at oss.nttdata.com> wrote:
>>>> 
>>>> I fixed my patch because it had unnecessary code that was pointed before.
>>>> I would appreciate if anyone could sponsor this patch.
>> 
>> I can sponsor the patch. I un-edited the line that assigns _body[0] to minimize the delta.
>> 
>> diff -r c29c9012c0ed src/hotspot/share/oops/symbol.cpp
>> --- a/src/hotspot/share/oops/symbol.cpp    Tue Jul 07 23:11:13 2020 -0700
>> +++ b/src/hotspot/share/oops/symbol.cpp    Wed Jul 08 11:25:48 2020 -0700
>> @@ -52,9 +52,7 @@
>>    _hash_and_refcount = pack_hash_and_refcount((short)os::random(), refcount);
>>    _length = length;
>>    _body[0] = 0;  // in case length == 0
>> -  for (int i = 0; i < length; i++) {
>> -    byte_at_put(i, name[i]);
>> -  }
>> +  memcpy(_body, name, length);
>>  }
>> 
> 
> Here's the webrev. Is everyone OK with it?
> 
> 8247818: GCC 10 warning stringop-overflow with symbol code
> Reviewed-by: kbarrett, iklam
> Contributed-by: sakatakui at oss.nttdata.com
> 
> http://cr.openjdk.java.net/~iklam/jdk16/8247818-symbol-gcc-warning.v01/

Looks good.

>> 
>>> What about this unaddressed comment?
>>> 
>>>> On Jul 7, 2020, at 10:36 AM, Kim Barrett <kim.barrett at oracle.com> wrote:
>>>> However, the first two elements of _body are used by identity_hash().
>>>> That seems like a possible reason to force initialization of both
>>>> elements, which currently isn't done for length == 1.  But maybe it
>>>> doesn't matter that identity_hash isn't consistent between processes,
>>>> in which case forcing the initialization of _body[0] also shouldn't
>>>> be needed.
>>> I think it’s a waste to initialize _body[0] or a bug to not initialize _body[1].
>>> I’ve no idea which.
>>> 
>> I think this should be done in a separate RFE. I filed
>> https://bugs.openjdk.java.net/browse/JDK-8249087
>> Symbol constructor unnecessarily initializes _body[0]

OK.