RFR: 8217717: ZGC: Broken oop map in C1 load barrier stub

Per Liden per.liden at oracle.com
Fri Jan 25 14:14:48 UTC 2019

Thanks for reviewing, Nils!


On 1/25/19 2:26 PM, Nils Eliasson wrote:
> Hi Per,
> Looks great!
> Regards,
> Nils
> On 2019-01-24 13:29, Per Liden wrote:
>> On 1/24/19 12:05 PM, Per Liden wrote:
>>> The C1 load barrier stub for ZGC can emit a patching area for a lea 
>>> instruction. However, the call into the VM to do the patching at this 
>>> site is not associated with a proper oop map. As a result, we can end 
>>> up with a stable oop in the base pointer register if a GC safepoint 
>>> happens 
>> s/stable/stale/ ;)
>>> when we enter the VM to patch.
>>> This problem is not super easy to reproduce by default, but is a 
>>> serious bug when it happens. However, it is fairly easy to reproduce 
>>> when also injecting a small delay in the 
>>> ZNMethodTable::register_nmethod().
>>> The proposed solution is to never allow patching to happen inside the 
>>> load barrier stub. Instead, if patching is needed, we emit the lea 
>>> instruction as part of the load preceding the load barrier. That will 
>>> automatically generate the proper oop map for the patch site.
>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8217717
>>> Webrev: http://cr.openjdk.java.net/~pliden/8217717/webrev.0
>>> Testing: Manual testing and inspection of generated code. Passes 
>>> gc-test-suite. Currently running tier1-3 on all platforms, and 
>>> tier1-7 on Linux/x86.
>>> /Per

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