RFR (S) 8203479: JFR enabled ARM32 build assertion failure
boris.ulasevich at bell-sw.com
Tue Jun 19 08:53:56 UTC 2018
On 19.06.2018 06:01, David Holmes wrote:
> Hi Boris,
> Looks good.
> I've pushed this with the single review as it is constrained to a
> non-Oracle port, and is very simple.
> On 18/06/2018 7:18 PM, Boris Ulasevich wrote:
>> Hi David,
>> Many thanks! Here is the werbev with updated copyrights:
>> On 18.06.2018 05:39, David Holmes wrote:
>>> Hi Boris,
>>> On 15/06/2018 8:44 PM, Boris Ulasevich wrote:
>>>> Please review the following patch:
>>>> Assertion fires in JFR codes on first VM thread setup because VM
>>>> globals are not yet initialized (and supports_cx8 property is not
>>>> predefined for ARM32 platform). I propose to exploit
>>>> early_initialize() method to set up supports_cx8 property on early
>>>> stage of VM initialization.
>>> Your fix looks good. Please update copyright years.
>>> Just some additional commentary ... from the bug report:
>>> First _supports_cx8 usage:
>>> Threads::create_vm -> JavaThread::JavaThread(bool) -->
>>> Thread::Thread() --> JfrThreadLocal::JfrThreadLocal() -->
>>> atomic_inc(unsigned long long volatile*)
>>> I'm not sure when this was introduced but it's risky to perform
>>> atomic operations on jlong early during VM initialization.
>> For me it comes from revision when JFR was opensourced:
>> changeset: 50113:caf115bb98ad
>> user: egahlin
>> date: Tue May 15 20:24:34 2018 +0200
>> summary: 8199712: Flight Recorder
>>> Apart from the problem you encountered with ARM32, on some platforms
>>> it may require that the stub-generator has been initialized. (Though
>>> in that case we may harmlessly fallback to using non-atomic
>>> operations - which is okay when creating the initial JavaThread.)
>> Good point! Yes, we discussed as an optional solution: (1) reworking
>> jfr next_thread_id() function to increase counter without atomic_inc
>> function call when counter value is zero, and (2) disable assertion
>> when !is_init_completed(). We decided that for our case initialization
>> sequence reorder works better.
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