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

[Andrew Haley]

On Mon, 29 May 2023 01:13:33 GMT, Hao Sun <haosun at openjdk.org> wrote:

> We thought it's the usual convention that any MacroAssembler call can clobber rscratch1 or rscratch2 registers. We
> cannot do that in protect_return_address() and authenticate_return_address(). Here shows an exception case [2]. We 
> may need revisit all the usages of rscratch1 and rscratch2 to check if this convention can be guaranteed.

Generally speaking, that is the rule. If LR is not live in the snippet you mentioned, we could use LR instead of rscratch1.

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PR Comment: https://git.openjdk.org/jdk/pull/13322#issuecomment-1566865984