RFR: JDK-8299229: Allow UseZGC with JVMCI and enable nmethod entry barrier support [v2]

[Erik Österlund]

On Fri, 20 Jan 2023 21:16:12 GMT, Tom Rodriguez <never at openjdk.org> wrote:

>> src/hotspot/share/jvmci/jvmciCodeInstaller.cpp line 732:
>> 
>>> 730: 
>>> 731:     if (UseZGC && _nmethod_entry_patch_offset == -1) {
>>> 732:       // ZGC requires the use of entry barriers for correctness
>> 
>> Note that G1 also requires nmethod entry barriers for correctness.
>
> We've been happily running without them for a long time which is why we're just now getting around to supporting them.  Are we sitting on a ticking time bomb?  I do want to make them required as of 21 but maybe we could defer that to a future commit once my Graal changes to support the entry barriers has landed?

Yeah unfortunately it is a ticking time bomb. Will you fix it for 21?

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PR Review Comment: https://git.openjdk.org/jdk/pull/11996#discussion_r1176482629