RFR: 8297967: Make frame::safe_for_sender safer [v6]

[Aleksey Shipilev]

On Fri, 2 Jun 2023 16:30:17 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Johannes Bechberger has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains four commits:
>> 
>>  - Remove errorneously added check
>>  - Remove check for value that might be null
>>  - More SafeFetch
>>  - Make frame::safe_for_sender safer with SafeFetch
>
> Some drive-by comments here.

> @shipilev do you think that bringing this PR is worthwhile? It only hardens the API when it is slightly misused (being passed in broken ucontexts).

In my mind, if this have a non-zero probability of happening during the normal non-fuzzing execution, then we should be on the safe side and check. A profiler that crashes the app is never a good thing. I got here through the [bug report here](https://github.com/corretto/corretto-11/issues/328) -- so it might be a signal that problems like these happen IRL.

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PR Comment: https://git.openjdk.org/jdk/pull/11461#issuecomment-1574152626