[riscv-port] RFR: 8279664: riscv: JFR crashes at 0x0 [v3]

[Xiaolin Zheng]

> Hi team,
> 
> This is a preview fix for the JFR-related crash - maybe the comment in this patch should be polished.
> TIL that complex problems often result from seemingly negligible changes :-)
> I need to cautiously test this change, though it seems no harm, to guarantee that it is safe and to ensure the problem is gone so please stay a little tuned.
> 
> ----
> Update:
> 
> 1. Overnight JFR testing reveals no error, seems fixed.
> 2. `test/hotspot/jtreg` on the board reveals no error until now - still testing, but I think it is safe.
> ----
> 
> Thanks,
> Xiaolin

Xiaolin Zheng has updated the pull request incrementally with one additional commit since the last revision:

  Polish comments

-------------

Changes:
  - all: https://git.openjdk.java.net/riscv-port/pull/49/files
  - new: https://git.openjdk.java.net/riscv-port/pull/49/files/9ae33721..dd8b495e

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=riscv-port&pr=49&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=riscv-port&pr=49&range=01-02

  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/riscv-port/pull/49.diff
  Fetch: git fetch https://git.openjdk.java.net/riscv-port pull/49/head:pull/49

PR: https://git.openjdk.java.net/riscv-port/pull/49