RFR: 8308503: AArch64: SIGILL when running with -XX:UseBranchProtection=pac-ret on hardware without PAC feature

[Hao Sun]

On Tue, 23 May 2023 16:14:21 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> Virtual threads are proposed to be a permanent feature in JDK 21 so I assume predicating this on Arguments:enable_preview check no longer make sense.
>
>> Virtual threads are proposed to be a permanent feature in JDK 21 so I assume predicating this on Arguments:enable_preview check no longer make sense.
> 
> Oh, I **see**. So it really only makes sense either to make ROP protection work in vthreads, or just disable ROP protection in JDK 21.

> I presume you didn't intend to change the logic here.

@theRealAph I suppose the logic is not changed yet. `_rop_protection` is initialized as "false" at line 457.

We enable it iff all the three conditions are satisfied at line 468.
Otherwise, one warning message is emitted if any condition is not met, i.e., line 463, line 466 and line 471.

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PR Review Comment: https://git.openjdk.org/jdk/pull/14095#discussion_r1203245944