RFR: 8313800: AArch64: SA stack walking code having trouble finding sender frame when invoking LambdaForms is involved [v2]

[Andrew Haley]

> This PR fixes a specific problem caused by using r29/rfp to unwind Java code. For some time we have treated r29 as a callee-saved scratch register, and it is freely used by C2-generated code. Therefore, any code in SA that uses getFP() in a compiled frame is very likely to come to grief.
> 
> I believe this is the root cause of 8313800, but it's very hard to prove that because because it's something of an intermittent fault.

Andrew Haley has updated the pull request incrementally with one additional commit since the last revision:

  Duplicated comment

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/15624/files
  - new: https://git.openjdk.org/jdk/pull/15624/files/486abc06..a8d14946

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15624&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15624&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 2 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/15624.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15624/head:pull/15624

PR: https://git.openjdk.org/jdk/pull/15624