How is the preempt stub be like?

[xtex]

Hi!

I am working on porting JEP-491 to LoongArch (it is not in the upstream 
OpenJDK, also I am not employed to do that, just an amateur).
I am trying to understand the code in [1].

When a monitorenter is called, StubAssembler::epilogue will be asked not to 
restore the stack pointer from frame pointer register.
The comment says "fp restored from the stub would be invalid" when the current 
frame is frozen. I wonder if there are any documentation about how does the 
freezing process happen and why FP is invalid but FP and return address (RA) 
loaded from the address pointed by SP is still valid?

Thanks!

[1] https://github.com/openjdk/jdk/pull/21565

-- 
xtex @ Mon, 20 Jan 2025 10:35:48 +0000
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