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

[Hao Sun]

On Thu, 6 Apr 2023 09:58:39 GMT, Hao Sun <haosun 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()?
>
>> 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.

> @shqking, to get a relative SP, I think you would want to subtract SP from thread->last_continuation()->entry_sp().

Thanks for your hint. I will take a try.

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PR Comment: https://git.openjdk.org/jdk/pull/13322#issuecomment-1499890789