[aarch64-port-dev ] jdk1 Fix for hotspot/test/gc/g1/TestJNIWeakG1/TestJNIWeakG1.java

[Stuart Monteith]

Ok,
  The assert I added to g1_write_barrier_post was tripping - we were
passing rscratch1 and using it locally. I could just change it to
rscratch2, but if we are passing temporary registers as parameters,
I'd argue we shouldn't be using rscratch1, etc, hardcoded in those
routines. In other platforms we are passing more than two temporary
registers. I'll have a look at a more extensive change.

BR,
   Stuart

On 16 August 2017 at 18:13, Stuart Monteith <stuart.monteith at linaro.org> wrote:
>  In  MacroAssembler::g1_write_barrier_pre I'm thinking:
>
> 3644   if (obj != noreg)
> 3645     assert_different_registers(obj, pre_val, tmp, rscratch1);
> 3646   else
> 3647     assert_different_registers(pre_val, tmp, rscratch1);
>
> However, I don't understand why that condition would be there and not just:
>    assert_different_registers(obj, pre_val, tmp, rscratch1);
> as the other registers ought not to be "noreg" - although there is a
> separate useful assert for pre_val.
>
> On the same principle, would it be acceptable to add the following in
> the same patch to MacroAssembler::g1_write_barrier_post?
>
> I've tried adding the following, but I'll need to get back to you as
> it might be tripping:
>     assert_different_registers(store_addr, new_val, thread, tmp, tmp2,
> rscratch1);
>
> BR,
>    Stuart
>
>
>
>
> On 16 August 2017 at 17:39, Andrew Haley <aph at redhat.com> wrote:
>> On 16/08/17 12:34, Stuart Monteith wrote:
>>> There was a bug introduced by "8176100 G1 Need prebarrier on deference
>>> of weak JNI handles" where a rscratch1 is being passed to
>>> g1_write_barrier_pre where it is already using rscratch1. This causes
>>> the TestJNIWeakG1 testcase to SIGSEGV as the temporary register is
>>> being used fro two conflicting purposes.
>>
>> We need an assert to make sure this doesn't happen again.
>>
>> --
>> Andrew Haley
>> Java Platform Lead Engineer
>> Red Hat UK Ltd. <https://www.redhat.com>
>> EAC8 43EB D3EF DB98 CC77 2FAD A5CD 6035 332F A671