RFR: 8286711: AArch64: serviceability agent tests fail with PAC enabled

[Chris Plummer]

On Fri, 20 May 2022 15:52:04 GMT, Nick Gasson <ngasson at openjdk.org> wrote:

> When the VM is run with `-XX:UseBranchProtection=pac-ret` on a supported CPU, the upper bits of the saved link register contain a "pointer authentication code" which must be checked and removed by a special instruction before a function returns.  The serviceability agent is unaware of this and so sees garbled PC values when walking the stack. This patch just masks out the PAC bits from the sender PC after reading it from the stack frame.

Marked as reviewed by cjplummer (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/8814