RFR: 8277948: AArch64: Print the correct native stack if -XX:+PreserveFramePointer when crash [v2]

[Denghui Dong]

On Tue, 18 Jan 2022 13:43:25 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> Denghui Dong has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   fix pfl() crash problem and rename from_thread to from_anchor
>
> So, here's my thinking for now. `_from_anchor` really means _this SP is trustworthy_, and perhaps we need a different name which suggests that. `sp_ok_to_use()` or `sp_is_trusted()` or somesuch? We do at least need a comment which explains that unless this boolean is true, the SP value in a frame is basically garbage, although it will point to somewhere within the stack. With that change, this patch can be integrated.
> In the longer term, I think we should look at using libunwind to obtain a precise native stack trace, and then we can get rid of all the old kludges.

@theRealAph 
Do you have other comments on the current patch?

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PR: https://git.openjdk.java.net/jdk/pull/6597