RFR: 8230401: ClassLoaderData::_keep_alive is read with wrong type in c2i entry barrier

[Erik Osterlund]

Hi Ioi,

Thanks for the review.

/Erik

> On 31 Aug 2019, at 05:13, Ioi Lam <ioi.lam at oracle.com> wrote:
> 
> Looks reasonable to me.
> 
> Thanks
> - Ioi
> 
>> On 8/30/19 8:43 AM, Erik Österlund wrote:
>> Hi,
>> 
>> Zhengyu noticed that the ClassLoaderData::_keep_alive field is a short, but the c2i entry barrier reads it with cmpl, treating it like an int.
>> 
>> First of all, thanks Zhengyu for spotting that. Nice catch.
>> 
>> Encoding cmpw is not currently supported for x86_64 extended registers, used in the barriers. So my proposed fix is to simply change the type of _keep_alive to int. Because the 2 extra bytes will become padding anyway, so we are not really saving any bytes by making it s2.
>> 
>> Bug:
>> https://bugs.openjdk.java.net/browse/JDK-8230401
>> 
>> Webrev:
>> http://cr.openjdk.java.net/~eosterlund/8230401/webrev.00/
>> 
>> Thanks,
>> /Erik
>