RFR: 8287325: AArch64: fix virtual threads with -XX:UseBranchProtection=pac-ret

[Hao Sun]

On Thu, 6 Apr 2023 00:25:29 GMT, Dean Long <dlong at openjdk.org> wrote:

> Using SP seems like the right way to go. Can't we compute the correct SP value to use in Runtime1::generate_handle_exception()?

Thanks for your question, Dean.
Thinking more about it, I guess we can get the expected SP value.

In my local test, I always use `rfp + 16` to authenticate the return address, and test cases under `test/jdk/java/lang/Thread/` and `test/hotspot/jtreg/compiler/c2/` can pass except the `virtual thread` cases. I'm running tier1-3 now.

My concern is that **using absolute SP** is incompatible with **virtual thread**, since PAC re-sign is still needed due to the stack copying process (See Requirement-2 in the commit message). Alternatively, we may want to use **relative SP** as the modifier.

However, I didn't know how to get such an **initial SP** value. Do you have any idea?
Thanks.

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PR Comment: https://git.openjdk.org/jdk/pull/13322#issuecomment-1498798117